Colour Theory

[KellyJohnston1]

Simple colour theory question - I'm stacking about 7 layers on top of each other and need a way to best see all of them where they overlap.  I was thinking the bottom layers need to be darker and ramp to lighter towards the top, adjusting transparency accordingly.  But, it isn't working very well. 

Any tips?

Thanks!

[847396730]

Seven layers is a tall order, but consider using gradients; here's a portion of a USFS index I made that expresses overlap.