What is the RGB co-ordinates of a colour at (0.25, 0.65, 0) in CMY space?

The CMY colour model is subtractive and is the complement of the additive RGB model: each RGB channel is obtained by subtracting the corresponding CMY value from 1 — R = 1 − C, G = 1 − M, B = 1 − Y — with every value expressed on the 0–1 scale.

1. R = 1 − C = 1 − 0.25 = 0.75

2. G = 1 − M = 1 − 0.65 = 0.35

3. B = 1 − Y = 1 − 0 = 1

Converting the result back with the inverse relation C = 1 − R, M = 1 − G, Y = 1 − B reproduces (0.25, 0.65, 0), confirming the conversion.

So the RGB co-ordinate is (0.75, 0.35, 1).