mix color

any body tell me how mix color
1:for ex if i want dark magenta value how this
i know the magenta gcolor3f(1.0,0.0,1.0)

2:again iwant get dark red color vaule
gcolor3f(1.0,0.0,0.0) this for red:confused:

To do colour mixing correctly you need to to convert your colours to a system such as HSL not RGB. To simply darken a colour, reduce each component by an equal percent; eg dark red (0.5,0,0) dark magenta (0.5,0,0.5)