Well first off the anemone would be the host, and second are your clowns picasso's(which would be a percula) or could they be snowflakes which would be occs.
Most clowns will accept most host nems, but it is preferable to have a natural host match.
I have had my picasso's almost 5 years now, and I have seen their black color fade when not in a natural host nem, LTA and BTA.
Upon removal of those nems their black came back.
So if this matters you may want to figure out exactly what your clowns are and seek a natural host nem, providing your tank can accomidate that.