See all console colors

[enum]::GetValues([System.ConsoleColor]) | Foreach-Object {Write-Host $_ -ForegroundColor $_}

Or to try every possible foreground/background combo:

$colors = [enum]::GetValues([System.ConsoleColor])
foreach( $fcolor in $colors )
{
	foreach( $bcolor in $colors )
	{
		Write-Host -NoNewLine "$fcolor/$bcolor "-ForegroundColor $fcolor -BackgroundColor $bcolor
	}
}
$host.ui.rawui.ForegroundColor = <ConsoleColor>
$host.ui.rawui.BackgroundColor = <ConsoleColor>
$Host.PrivateData.ErrorForegroundColor = <ConsoleColor>
$Host.PrivateData.ErrorBackgroundColor = <ConsoleColor>
$Host.PrivateData.WarningForegroundColor = <ConsoleColor>
$Host.PrivateData.WarningBackgroundColor = <ConsoleColor>
$Host.PrivateData.DebugForegroundColor = <ConsoleColor>
$Host.PrivateData.DebugBackgroundColor = <ConsoleColor>
$Host.PrivateData.VerboseForegroundColor = <ConsoleColor>
$Host.PrivateData.VerboseBackgroundColor = <ConsoleColor>
$Host.PrivateData.ProgressForegroundColor = <ConsoleColor>
$Host.PrivateData.ProgressBackgroundColor = <ConsoleColor>

$host.ui.rawui
$host.ui.rawui | select *color

Get-PSReadlineOption
Get-PSReadlineOption | Select *color

$Host.PrivateData

I seem to have some groovy write-host replacement installed called 'Pansies' that means i can express colors in hex rgb, so this produces some nice tones:

1..9 | % { 
	$R = $_; 1..9 | % { 
		$G = $_; 1..9 | % { 
			$B = $_; 
			write-host " $($R)$($R)$($G)$($G)$($B)$($B)" -f "#$($R)$($R)$($G)$($G)$($B)$($B)" -n 
		}
	}
}

Oh - it has some other methods that are useful too:

which * | ? { $_.Source -eq "Pansies" }

CommandType     Name                                               Version    Source
-----------     ----                                               -------    ------
Alias           Text -> New-Text                                   2.0.0      Pansies
Cmdlet          Get-ColorWheel                                     2.0.0      Pansies
Cmdlet          Get-Complement                                     2.0.0      Pansies
Cmdlet          Get-Gradient                                       2.0.0      Pansies
Cmdlet          New-Text                                           2.0.0      Pansies
Cmdlet          Write-Host                                         2.0.0      Pansies

e.g.

> get-complement "red"

Mode           RGB (hex) X11ColorName         Ordinals                  XTerm Index ConsoleColor
----           --------- ------------         --------                  ----------- ------------
Automatic      #00FFFF   Cyan                 R=0.000; G=255; B=255     14          Cyan

Source