It probably isn't getting enough nutrients/vitamins to keep it's color.
Silversides are good but ghost shrimp aren't IMO. I recommend to use garlic extract on the food. Mine likes it and it's healthy for them.
I feed my lion raw shrimp w/o shell (like you buy at a grocery store), silversides, octopuss (beware of ink sack), krill (but only when it steals it from what I givce my scorpion), and recently ate a cube of angel/butterfly diet (i almost lost a finger :scared: ). I going to try frozen squid and formula 1 next.
Moral of the story...offer the lion one of the first three food sources mentioned above soaked in a bit of garlic and occaisionally some zoe or vitachem. Make sure the pieces are not too big for the lion to eat. If it resists the new food types, wait 2-3 days to offer it again. Most lions will eat whatever they can fit in their mouth.