The kanji 色 depicts a kneeling person with emphasis on their complexion or expression. This reveals their 'color' (of emotion) or general 'hue', and historically, the character also conveyed concepts of beauty or sexual desire, leading to the meaning of 'lust'.
'Iro' — Sounds like 'E-ROH'. Think of 'erotic' or 'romantic' to remember its meanings of 'lust' and 'colorful' passion.
'Shoku' — Sounds like 'SHOW-ku'. Imagine a 'show' of amazing 'colors'.