Lora, судя по цифрам на ваших рисунках, чуть по другому:
С = 0 * 100 = 0%............C = (1-R/255)*100% = (1-255/255)*100% = 0%
M = 1 * 100 = 100%..........M = (1-G/255)*100% = (1-0/255)*100% = 100%
Y = 0.498 * 100 = 49.8%.....Y = (1-B/255)*100% = (1-128/255)*100% = 49.8039..%
K = 0 * 100 = 0% =..........Что такое "К" не знаю