My lover/master and I use the traffic lights, in general. I know that, as a sub, I look at those words as both safety and a challenge: if I need them, they are there, but how far can I push myself before I use one? So far, I only used an out over something I could not control, like needing the bathroom--neither of us is into water/mud play.
As far as my l/m has expressed his feelings about them to me, well, when I told him that I held back using my yellow/red, he was almost angry. He wants me to have those words for my safety, and should not hesitate to use them.
I did, in a story I started writing, come up with some extra color words to give more detail: Blue means I need a drink, brown is for the bathroom, grey for a cigarette. In the story, I was topping him, and warning him it would be a long session, so he might need the others before we were done. It seems silly in light of this thread.
Hope this adds to the discussion.