[feat] YPbPr Color model

[logaretm]

Implement YPbPr color model fns.

also written as YPBPR, is a color space used in video electronics, in particular in reference to component video cables. YPbPr is the analog version of the YCbCr color space; the two are numerically equivalent but YPbPr is designed for use in analog systems while YCbCr is intended for digital video. YPbPr is commonly referred to as component video by manufacturers; however, there are many types of component video, most of which are some form of RGB. Some video cards come with video-in video-out (VIVO) ports for connecting to component video devices.

This is not a supported CSS format, so I guess its format should follow the others by convention, otherwise, if there is an established convention to represent a YPbPr value it should be used as its parse and format targets.