Hello! Welcome to the forum.
I wouldn't be doing my due diligence if I didn't ask these questions (that are seemingly unrelated), so please bear with me. Please provide the following:
Tank Size
Tank mates:
Water Parameters: pH, Ammonia, Nitrite, Nitrate
Length that tank has been established:
Tank mates?
Your flowerhorns diet with vary to an extent based on what type of food it is accepting (flake v. pellets)
Typically, a mixture of live/frozen foods will always help increase color and health of the fish. Additionally, I would look for high protein foods that are also high in beta carotenoids. I have heard good things about Hikari color enhancing pellet foods and I have personally seen great results from the Omega One line of color enhancing foods.