It's yellow.
It's a good idea: I've seen this idea thrown around in various LS's.
I'd also like to throw out that while RPC is a small fraction of the community, there's nothing from stopping people from spreading the word to various LS's. Heck even shout once in a while at hubs would work, I would think. Word of mouth is a powerful tool, and something as simple as this doesn't need a long explanation. And if people don't want to use it, no big deal.