Frogspawn don't really lose their color. When they are dying they retract in to the skeleton, then eventually they just disappear at those parts. You should look at the receded parts and see if there is anything that looks like brown jelly, that is a disease. If the rest of the frogspawn looks fine other than 1 or 2 dead heads, you can just leave the head or you can cut it off to make the whole thing look better. If the whole piece looks like a skeleton then it is dead.