SSSSOOOOO.....
Right, your thinking what is this idiot on about? Okay,so it makes a BBBBIIIIGGGG difference. Are you really going to put blue on yellow? Hhrrmm, no. Just no. The colour should represent the book, (I know I've already said this blah, blah, blah...) Heres a little test to see what I mean, your going to read these words and think of which colour you feel it represents. Okay, lets try to steer you off course:
MONDAY
WEDNESDAY
TUESDAY
FRIDAY
DOUGHNUT
THURSDAY
SATURDAY
SUNDAY
APPLE
BOAT
LOLLIPOP
CORK
DUMMY
BABY
MMMOOOOOOO
COW
SHEEP
PIG
YELLOW
BLUE
Really wierd right? Okay, so if its your story like mine then you should think colours for it like: LONELY, SEA, WAR, PEACE, LOVE, FRIENDSHIP, CURIOUS, TRIBES, FIRE, DANCING, SICKNESS, HAPPINESS, SLAVERY, WILL, EMOTION, PEACEFULNESS, EMPATHY, DARING.
That's the colours, but you have to make sure that they don't clash with the rest of the cover, (Yellow writing on a blue page? uuuurrrrgggghhhh, please no.) Also, the gradiation. If you have orangey pastel writing, then maybe only change the gradiation a couple of shades. Make the most important words stand out, the title is best if it is slightly bigger and, if you have the authors name on there as well, then don't make it too loud or swirly because so many big things on a page can make it look a bit messy and weird.