i voted for black leather, but my answer is generally "dark". i get that it shows dust/dirt more than lighter interiors, but i cannot deal with (what i feel is the additional) reflection of sunlight onto a light dash/interior. it just screws with my eyes. i prefer the interior of the car to be dark for contrast.
My last car had tan leather interior and it got really dingey and gross looking after a while. Also during the summer it was still a literal PITA to sit on.
My car now has gray cloth interior and I like it better.
I have off white leather in my car, and it's just as beautiful as the day I bought it. I've had 2 other cars with black leather and will never have it again - too hot.
Black leather is a must have for me. Anything lighter on whatever material shows too much dirt, scuffs, spills, & marks. I park in garages at home and work and only sometimes outside so the sun/heat factor doesn't bother me.
I have grey leather and I really like it. I remember when I was buying a car 9 years ago, I really wanted the grey leather, since most of the light blue Solaras came with the dark tan leather, which I didn't really care for. Finally found my grey and I love it. I have a very strong preference for leather because I loooove having heated seats in the winter. When DH bought his Elantra last year, I kind of insisted that he get the Limited edition just for the leather.