Virtual terminal queries (DECRQSS) return values as INPUT but allow us to test support for syntax

Get-ColorMode.ps1

function Get-ColorMode {
    <#
        .SYNOPSIS
            Tests for FullColor (RGB) mode and X11/XTerm (XColor) modes by writing SGR and verifying it with a DECRQSS
            Returns "Uknown" if there's no DECRQSS support, or "FullColor" and/or "XColor" otherwise
        .NOTES
            See the XTerm FAQ for details on why some terminals use ; (to be compatible with a mistake made by XTerm)
            https://invisible-island.net/xterm/xterm.faq.html#color_by_number

            See the ISO-8613-6 standard for details on the ODA color modes
            Free Here: https://www.itu.int/rec/T-REC-T.416-199303-I/en

            I've never seen a full implementation of ODA's SGR codes in a terminal. It would have 7 parameters:

            Foreground: ESC[38:Ps:Pi:P3:P4:P5:P6:P7:P8m 
            Fackground: ESC[48:Ps:Pi:P3:P4:P5:P6:P7:P8m 

            Where Ps is the color space (*and I've only ever seen 2 and 5 implemented)
            0 = Implementation Defined (the default foreground color)
            1 = Transparent
            2 = RGB
            3 = CMY
            4 = CMYK
            5 = Indexed (In terminals, this _almost always_ means XTerm's 256 colors)

            For Ps = 0 or 1 there would be no other parameters.
            For Ps = 5 there is only Pi: the index of the color in the palette (0-255)
            For Ps = 2, 3, or 4, 
                the Pi parameter hypothetically specifies a colour space 
                defined in the document profile ... which of course does not exist in a terminal
                This parameter is therefore ignored and expected to be empty by most terminals
                The P7 is supposed to indicate a integer tolerance value
                The P8 is supposed to indicate a color space associated with the tolerance (0 for CIELUV, 1 for CIELAB)

            The most common case is Ps = 2, where the expected parameters are:
                P3 = Red (0-255)
                P4 = Green (0-255)
                P5 = Blue (0-255)
                P6 has no meaning

            Per the specification
                For Ps = 3 and 4:
                P3 = Cyan
                P4 = Magenta
                P5 = Yellow
                P6 = Black (but only for Ps = 4)
            In MinTTY the 2nd parameter, Pi is the max value for the color channels (So you can use 0-100 or 0-255)
    #>
    [CmdletBinding()]
    param()

    $ColorMode = [Ordered]@{
        '48;2;255;0;255'        = @{Name = 'FullColorCompatible' } # Konsole Compatible
        '48;5;254'              = @{Name = 'XColorCompatible' }    # Konsole Compatible
        '48:5:254'              = @{Name = 'ODA-XColor' }          # ISO-8613-6 indexed color space
        '48:2:255:0:255'        = @{Name = 'ITU-RGB' }             
        '48:2::255:0:255'       = @{Name = 'ODA-RGB' }             # XTerm's ISO-8613-6 implementation with no Pi
        # MinTTY supports CMY(K) format, and uses Pi to specifying the maximum value for color channels (e.g. 100 or 255)
        '48:3:255:255:0:255'    = @{Name = 'ODA-CMY';      AsRgb = '48:2::0:255:0' } # mintty accepts CMY(K) but returns RGB
        '48:4:255:255:0:255:255'= @{Name = 'ODA-CMYK';     AsRgb = '48:2::0:255:0' } # mintty accepts CMY(K) but returns RGB
        '48:3:100:100:0:100'    = @{Name = 'ODA-FlexCMY';  AsRgb = '48:2::0:255:0' } # mintty accepts CMY(K) but returns RGB
        '48:3:100:100:0:100:50' = @{Name = 'ODA-FlexCMYK'; AsRgb = '48:2::0:255:0' } # mintty accepts CMY(K) but returns RGB
    }
    
    $SupportedModes = @(foreach ($SGR in $ColorMode.Keys) {
            $DECRQSS = -join @(
                # Set the background color
                "`e[0m`e[$($SGR)m"
                # Output the DECRQSS SGR query https://vt100.net/docs/vt510-rm/DECRQSS.html
                "`eP`$qm`e`\"
                # Reset the background
                "`e[49m"
            )

            [console]::write($DECRQSS)
            Start-Sleep -milli 25 # I'm sorry, but sometimes it doesn't respond fast enough
            $Response = @(while ([console]::KeyAvailable) { [console]::ReadKey($true).KeyChar }) -join ""

            # Strip the DCS and ST from the ends of the response and return just the SGR value as the Response
            $Result, $Code = $Response -replace '^(?:\u001BP|\u0090)(\d+)\$r(?:0;)?(.*)m[\u001B\\\t]+$', '$1,$2' -split ','

            Write-Debug "QUERY: 'm' RESPONSE: '$($Result)r$($Code)m'"

            # the result code is supposed to be 1 no matter what, no idea what other values represent, really
            if ($Result -ne 1) {
                Write-Verbose "Request Status String (DECRQSS) not supported (returned '$Result')"
                continue
            }
            if ($Code -ne $SGR) {
                Write-Verbose "Unexpected Response. We set '$SGR' but received '$Code'."
                # The department of second chances.
                # Terminals generally return their prefered separator, even if they handle both ; and :
                # Windows Terminal apparently treats : separated SGR as ODA T.416 format 
                # See: 
                # Except they do not support color modes, so it just has an empty spot
                # E.g. it returns 48:2::R:G:B where it should be 48:2:2:R:G:B
                if (($SGR -replace '[;:]+', ':') -ne ($Code -replace '[;:]+', ':') -and $Code -ne $ColorMode[$SGR].AsRgb) { 
                    continue
                }
            }
            Write-Verbose "Working. We set '$SGR' and received '$Code'."
            $SGR
        })
    $ColorMode[$SupportedModes].Name
}

Get-VtResponse.ps1

function Get-VtResponse {
    <#
        .SYNOPSIS
            Write a VT ANSI escape sequence to the host and capture the response
        .EXAMPLE
            $Row, $Col = (Get-VtResponse "`e[6n") -split ';' -replace "[`e\[R]"

            Gets the current cursor position into $Row and $Col
    #>
    [CmdletBinding()]
    param(
        [Parameter(Mandatory)]
        $Sequence
    )
    [console]::write($sequence)
    Start-Sleep -milli 5 # I'm sorry, but sometimes it doesn't respond fast enough
    @(while ([console]::KeyAvailable) {
        [console]::ReadKey($true).KeyChar
    }) -join ""
}