Hmm..... then perhaps a new name for the keyword would be nice.
I'm really not a fan of making keyword mechanics exclusive to one color. Ravinca Block did the whole "one per guild" thing and it was nice for flavor and all, but it flooded the game with too many mechanics. I was a big fan of when there was 2 new mechanics per block. Mirage Block - Phasing and Flanking; Rath Cycle - Buyback and Shadow; Urza's Cycle - Cycle and Echo; etc.
Sorry, I seemed to have ranted off in a tangent. But the point I'm trying to make is if we make a keyword exclusive to one color, it has to be balanced out somewhere. I really don't want to see exclusive mechanics in our set, so lemme change this......
Duck/Tunnel/Shelter (<this> can not be blocked by creatures with flying)
Ransac, cpa trash man