Are the Registration Colors are supported by Prince?

I don't think so. What exactly do you require?

We need functionality similar to this one - I hope this example can better explain my question.

http://www.websupergoo.com/helppdfnet/source/5-abcpdf/doc/1-methods/addcolorspacespot.htm

You can define separation colors with this at-rule

@prince-color Gold {
    alternate-color: cmyk(0, 0, 1, 0) /* can be rgb() for display purposes */
}

Then you can use it in color values with an optional tint:

body { color: prince-color(Gold) }
body { color: prince-color(Gold, 50%) }