PowerShell example using an enumerator type to map colour name to value with a default value set for invalid values

Convert-ColourNameToColourValueEnumeratorTypeWithDefault.ps1

$colourName = 'grey'

# Only needs to be declared once
enum colour {
    red = 0xFF0000 
    green = 0x00FF00
    blue = 0x0000FF
    white = 0xFFFFFF
}

$colourValue = [colour]::white

if (-not [colour]::TryParse($colourName, $true, [ref] $colourValue)) {
    return 0x0
} else {
    return $colourValue.value__
}