I think that you're overselling the benefits it gives you. They just aren't that powerful; certainly nowhere near as good as a bonus feat and extra skill points. In an underground campaign, Blue due to the massive Hide bonus, but outside of that their benefits really are quite minor and situational.
Hmm. That's true; free rerolls are rare and useful. All right, then Blue without buyoff and Cyan with.I think with the reroll/compulsion, they're blue/low end of light blue. Rerolls are golden in D&D, and to get one racially 1/day is pretty nice.
No. They have a +3 LA; you can't even buy off the first point of LA until level 9. I think you're overestimating the usefulness of buyoff and their abilities; it just isn't worth the +3 LA, even with buyoff.With buyoff, and an underground campaign, I'd say black/low blue. Otherwise red.