Zooanthid White Spots

Any known causes for white powdery-looking dust to form on oral disks?  I've had two medium colonies and one small frag of green eye variety for about 5mo in a 135gal (setup for 8mo). 

All have done well until about a month ago when two of the three started showing this white powdery look to their oral disks.  Third colony is still unaffected.  Is this an indication of too intense lighting?  If so, doesn't make sense that they all don't have it.  All are subject to same lighting (250w/20K MH).

You can see photos of an example of the normal one here:

http://www.foreverflying.com/Zoanthids-Green4.JPG

...and the one with the white powdery look here:

http://www.foreverflying.com/Zoanthids-Green3.JPG

If these are indications of light burn what steps should be taken (if any besides providing less intense lighting).

Thanks,

Can you wipe the "dust" off?.., they could have just changed color because of your intense lighting..., I had these ugly brown zoos in my tank when I first stated and I gave a couple to centipede and they went from brown to one of the most awsome light blue colored zoos..., they went from my week 36w 50/50 PC's to his 250W MH..., just a thought

Xacttech wrote: Just a color morph, I have some that look the same as those and did the same thing also. Nothing to wory about.

What size tank & lighting conditions do you have for yours that caused the same color morph?