Vladimir Averkin’s http://blogs.msdn.com/b/powershell/archive/2009/01/11/colorized-capture-of-console-screen-in-html-and-rtf.aspx provides the code.  Here’s the core magic.

$Host.UI.RawUI.GetBufferContents(System.Management.Automation.Host.Rectangle) will return a two-dimensional character array of the contents of the buffer.

This entry cleans up the HTML function by creating XML instead of using System.Text.StringBuilder to append strings.  Sadly, I don’t know RTF at all, so this is merely a merging of that code into a single function.

# .synopsis
# Capture console screen buffer.
#
# .returns
# HTML File
#
# .example
# PSH> Get-ConsoleBufferAsHtml
#
# C:\Users\timdunn\AppData\Local\Temp\Console-2013-09-20_150204.html
#
# .Notes
# See http://blogs.msdn.com/b/powershell/archive/2009/01/11/colorized-capture-of-console-screen-in-html-and-rtf.aspx
#
# .param Path
# Path to save screen buffer as HTML.  Defaults to "$env:TEMP\Console-<datestamp>", with suffix as appropriate to file format.
#
# .param Full
# Save entire console buffer.  Default is to only capture the current window.
#
# .param Preview
# Open the file in the default handler upon successful capture.
#
# .param HTML
# Save console buffer in HTML format.  Default is to save in ASCII.
#
# .param RTF
# Save console buffer in RTF format.  Default is to save in ASCII.
#
# .param Test
# Generate test pattern, save to file, then display files.

param (
     [string]$Path = "$env:temp\Console-$(Get-Date -Format yyyy-MM-dd_HHmmss).",
     [switch]$Full,
     [switch]$Preview,
     [switch]$HTML,
     [switch]$RTF,
     [switch]$Test
);

function Get-ConsoleBuffer {
     #region header
    
     param (
         [string]$Path = "$env:temp\Console-$(Get-Date -Format yyyy-MM-dd_HHmmss).",
         [switch]$Full,
         [switch]$Preview,
         [switch]$HTML,
         [switch]$RTF,
         [bool]$_boolFull    = $false,
         [bool]$_boolPreview = $false,
         [bool]$_boolHTML    = $false,
         [bool]$_boolRTF     = $false
     );

    #endregion
     #region html functions

     # The Windows PowerShell console host redefines DarkYellow and DarkMagenta colors and uses them as defaults.
     # The redefined colors do not correspond to the color names used in HTML, so they need to be mapped to digital color codes.
     function Normalize-HtmlColor ($color) {
         if     ($color -eq "DarkYellow")  { "#eeedf0"; }
         elseif ($color -eq "DarkMagenta") { "#012456"; }
         else                              { $color; }
     }

     function Add-HtmlSpan ($Text, $ForegroundColor = "DarkYellow", $BackgroundColor = "DarkMagenta") {
         $ForegroundColor= Normalize-HtmlColor $ForegroundColor;
         $BackgroundColor= Normalize-HtmlColor $BackgroundColor;

         $node = $script:xml.CreateElement("span");
         $node.SetAttribute('style', "font-family:Courier New;color:$ForegroundColor;background:$backgroundColor");
         $node.InnerText = $text;
         $script:xml.LastChild.AppendChild($node) | Out-Null;
     }

     function Add-HtmlBreak { $script:xml.LastChild.AppendChild($script:xml.CreateElement("br")) | Out-Null; }

     #endregion
     #region rtf functions
  
     function Get-RtfColorIndex ([string]$color) { 
         switch ($color) { 
             'DarkBlue'    {  2 } 
             'DarkGreen'   {  3 } 
             'DarkCyan'    {  4 } 
             'DarkRed'     {  5 } 
             'DarkMagenta' {  6 } 
             'DarkYellow'  {  7 } 
             'Gray'        {  8 } 
             'DarkGray'    {  9 } 
             'Blue'        { 10 } 
             'Green'       { 11 } 
             'Cyan'        { 12 } 
             'Red'         { 13 } 
             'Magenta'     { 14 } 
             'Yellow'      { 15 } 
             'White'       { 16 } 
             'Black'       { 17 } 
             default       {  0 } 
         } 
     } 
     function New-RtfBuilder {
         # Initialize the RTF string builder.
         $script:rtfBuilder = new-object system.text.stringbuilder

         # Set the desired font
         $fontName = 'Lucida Console'
         & { 
             # Append RTF header
             $script:rtfBuilder.Append("{\rtf1\fbidis\ansi\ansicpg1252\deff0\deflang1033{\fonttbl{\f0\fnil\fcharset0 $fontName;}}")
             $script:rtfBuilder.Append("`r`n")

             # Append RTF color table which will contain all Powershell console colors.
             # script version
             $script:rtfBuilder.Append('{\colortbl;red0\green0\blue128;\red0\green128\blue0;\red0\green128\blue128;\red128\green0\blue0;\red1\green36\blue86;\red238\green237\blue240;\red192\green192\blue192;\red128\green128\blue128;\red0\green0\blue255;\red0\green255\blue0;\red0\green255\blue255;\red255\green0\blue0;\red255\green0\blue255;\red255\green255\blue0;\red255\green255\blue255;\red0\green0\blue0;}') 
            
             # Append RTF document settings.
             $script:rtfBuilder.Append('\viewkind4\uc1\pard\ltrpar\f0\fs23 ')
         } | Out-Null;
     }

     # Append line break to RTF builder
     function Add-RtfBreak { 
         $script:rtfBuilder.Append("\shading0\cbpat$(Get-RtfColorIndex $currentBackgroundColor)\par`r`n") | Out-Null;
     }
    
     # append text to RTF builder
     function Add-RtfBlock ($Text, $ForegroundColor = "DarkYellow", $BackgroundColor = "DarkMagenta") {
         $ForegroundColor= Get-RtfColorIndex $ForegroundColor;
         $BackgroundColor= Get-RtfColorIndex $BackgroundColor;
        
         $script:rtfBuilder.Append("{\cf$ForegroundColor") | Out-Null;
         $script:rtfBuilder.Append("\chshdng0\chcbpat$BackgroundColor") | Out-Null;
         $script:rtfBuilder.Append("$Text}") | Out-Null;        
     }

     #endregion
     #region core code

     # Check the host name and exit if the host is not the Windows PowerShell console host.
     if ($host.Name -ne 'ConsoleHost') {
         Write-Warning "$((Get-Variable -ValueOnly -Name MyInvocation).MyCommand)runs only in the console host. You cannot run this script in $($Host.Name).";
         return;
     }
    
     # handle [switch] parameters in nested functions
     if (!$Full)    { $Full    = $_boolFull; }
     if (!$Preview) { $Preview = $_boolPreview; }
     if (!$HTML)    { $HTML    = $_boolHTML; }
     if (!$RTF)     { $RTF     = $_boolRTF; }

     # initialize document name and object
     if ($HTML) { 
         [xml]$script:xml = "<pre style='MARGIN: 0in 10pt 0in;line-height:normal' />";
         $Path += 'html';
         $RTF = $false;
     }
     elseif ($RTF) { 
         New-RtfBuilder; 
         $Path += 'rtf';
     }
     else {
         $fileBuilder = New-Object system.Text.StringBuilder;
         $Path += 'txt';
     }

     # Grab the console screen buffer contents using the Host console API.
     $bufferWidth = $Host.UI.RawUI.BufferSize.Width
     $bufferHeight = $Host.UI.RawUI.CursorPosition.Y

     # Line at which capture starts is either top of buffer or top of window.
     if ($Full) { $startY = 0; }
     elseif (($startY = $bufferHeight - $Host.UI.RawUI.WindowSize.Height) -lt 0) { $startY = 0; }

     $rec =  New-Object System.Management.Automation.Host.Rectangle 0,$startY,($bufferWidth - 1),$bufferHeight
     $buffer = $Host.UI.RawUI.GetBufferContents($rec);

     # Iterate through the lines in the console buffer.
     for($i = 0; $i -lt $bufferHeight; $i++)
     {
         $stringBuilder = New-Object System.Text.StringBuilder;

         if ($HTML -or $RTF) {
             # Track the colors to identify spans of text with the same formatting.
             $currentForegroundColor = $buffer[$i, 0].ForegroundColor;
             $currentBackgroundColor = $buffer[$i, 0].BackgroundColor;
         }

         for($j = 0; $j -lt $bufferWidth; $j++) {
             $cell = $buffer[$i,$j];

             # If the colors change, generate an HTML span and append it to the HTML string builder.
             if (($HTML -or $RTF) -and (($cell.ForegroundColor -ne $currentForegroundColor) -or ($cell.BackgroundColor -ne $currentBackgroundColor))) {

                 if ($HTML)    { Add-HtmlSpan -Text $stringBuilder.ToString() -ForegroundColor $currentForegroundColor -BackgroundColor $currentBackgroundColor; }
                 elseif ($RTF) { Add-RtfBlock -Text $stringBuilder.ToString() -ForegroundColor $currentForegroundColor -BackgroundColor $currentBackgroundColor; }

                 # Reset the span builder and colors.
                 $stringBuilder = New-Object System.Text.StringBuilder;
                 $currentForegroundColor = $cell.ForegroundColor;
                 $currentBackgroundColor = $cell.BackgroundColor;
             }

             if ($RTF) {
                 switch ($cell.Character)  { 
                     "`t"    { $rtfChar = '\tab' } 
                     '\'     { $rtfChar = '\\' } 
                     '{'     { $rtfChar = '\{' } 
                     '}'     { $rtfChar = '\}' } 
                     default { $rtfChar = $cell.Character; }
                 } 

                 $stringBuilder.Append($rtfChar) | Out-Null;
             }
             else {  $stringBuilder.Append($cell.Character) | Out-Null; }
         }

         if ($HTML) {
             Add-HtmlSpan -Text $stringBuilder.ToString() -ForegroundColor $currentForegroundColor -BackgroundColor $currentBackgroundColor;
             Add-HtmlBreak;
         }
         elseif ($RTF) {
             Add-RtfBlock -Text $stringBuilder.ToString() -ForegroundColor $currentForegroundColor -BackgroundColor $currentBackgroundColor;
             Add-RtfBreak;
         }
         else {
             $fileBuilder.Append(($stringBuilder.ToString() -replace ".$", "`r`n")) | Out-Null;
         }
     }

     & {
         if     ($HTML) { $script:xml.OuterXml; }
         elseif ($RTF)  { $script:rtfBuilder.ToString() + '}'; }
         else { $fileBuilder.ToString(); }
     } | Out-File -FilePath $Path -Encoding ascii;
    
     if (Test-Path -Path $Path) {
         if ($Preview) { Invoke-Item $Path; }
         $Path;
     }
     else { Write-Warning "Unable to save to -Path $Path"; }

     #endregion
}

#  if we execute this file instead of dot-source it
if ($MyInvocation.invocationName -ne '.') { 
  
     if ($Test) {
         [System.Enum]::GetValues('System.ConsoleColor') | % { Write-Host ((" " + $_.ToString() + (" " * 8)).SubString(0,11) + " ") -NoNewline; }
         Write-Host '';
         foreach ($f in [System.Enum]::GetValues('System.ConsoleColor') ) { 
            foreach ($b in [System.Enum]::GetValues('System.ConsoleColor')) { 
                 Write-Host -ForegroundColor $f -BackgroundColor $b " $($f.tostring().substring(0,3)) on $($b.tostring().substring(0,3)) " -NoNewline;
             } 
             Write-Host '';
         }

         & { 
             Get-ConsoleBuffer -HTML;
             Get-ConsoleBuffer -RTF;
             Get-ConsoleBuffer;
         } | % {
             Invoke-Item $_;
             Out-Host -InputObject $_;
         }
     }
     else {
         Get-ConsoleBuffer -_boolFull $Full -_boolHtml $HTML -_boolRTF $RTF -_boolPreview $Preview -Path $Path;
     }
}