i have been doing a lot of reading on anemones lately, and from what i read, the dark green or brown sebae's are the healthiest. what fluff said is right (as usual) and the white ones are usually bleached or dying.
sebae's are the anemone that will host the most types of clowns, but it is always a gamble, as your clown and anemone might never get together.
also, you might want to indicate what your tank size is and what your lighting situation is...
~mike