Every int parameter works for decimal, binary and hex. Underscore (_) digit separator is supported.
See supported color names and their values for Color.?, KnownColor.? and Color.FromName("?")here and here. That's all of them, except for Transparent and Empty, which does not make sense to be supported in this extension. System colors are not OS theme sensitive, their values are fixed based on the mono implementation.
Feel free to open any issues or pull requests. I will try to make time for them, if any.
Color.FromARGB(int, Color) when Color is highlighted.