I heard this on NPR,a while back but ,missed the answer.
What five letter,word means red.If you change the first letter,it still means red.If you change the first letter again,it means a totally differant word.
I think that's it.(sorry)

I think it went like this:
Start with a five letter word that means "red."
Change its first letter to get a different five letter word
that also means "red."
Finally drop the first letter to get a word that means "green."

Blush -> Flush -> Lush

Thanks for that, Ive be thinking of that for a while.