OMG, majka_ze, what a fantastic site!
twinmomgirl, I've randomly picked a few colours that may go with the brown & tan: CA9298, B6CA92, 92BFCA or perhaps the dusty pink you used as on the box of your shoe box cake or a dustier blue than what you used on your gold gift box? What event is it for? maybe that'll help with choosing a colour?
Brown and tan are really neutral colours to work with so you can petty much do anything...what kind of cake is it? Think about the theme and draw your inspiration from what the cake is actually for, like is it for a wedding, birthday, child, baby..etc. that's what i usually do. I'm sure whatever you choose will be great as long as the intensity of the colours is the same. Good luck, i'd love to see what you come up with...and i'm really curious as to what kind of cake your making!!! have fun!