Same thing happened to my frogspawn and hammer. They were a deep rich green with pink tips. Then slowly over time they lost color and the tips turn white. It is known as bleaching. Check your temp in your tank. Don't trust your thermometer! Try a few different thermometers and see if they all read the same.
My thermometer I had said my tank was around 76-79 all the time. I thought, "Great, temp isn't my problem!" So I started checking my water conditions. Alkalinity was in the 7's, which is low but not enough to casue bleaching, IMO. Calcium was in the 380-450 range depending on the week. Salinity was fine also. Then one day it hit me to check the temp of my tank with other thermometers. One thermometer read 84 while mine was reading 79!!!
So long story short check your temp first. That was my problem. It has now been two months since I solved my heat problem and both corals are getting their color back!
p.s. - I agree with Mark though too. Check all parameters and then listen to him on what to do! I was just telling you what worked for me!