I originally assumed you'd have to follow suit but from what I can tell from the rules the color of the cards has no gameplay consequence. Is that correct?
The game seems really interesting. I'm shocked it hasn't come out in the USA considering how popular Fairy Tale is.
The colors have their meanings,
Cards in green are citizen/kings, they are all about VPs,
Cards in blue are characters on the field/with magic, always let you draw cards,
Cards in pink are characters in exile and always requires others to discard,
Cards in yellow are only functioning on cards played on the table.
With colors you will easily remember their functions.