I think some of the healers use greenish spells so it is somewhat easy to pick out.
I used to do that on my Resto druid, I finally got exalted with wsg in wotlk.
I did this one my monk 2 days ago. I capped the flag then after that my team could not kill the other guy so I held the flag till like 10 stacks and they finally killed me, but they killed the other guy at the same time. 60% resilience for everyone has made our damage a bit weaker though:/.