You won't see much color at 4 months, but that is a good time to start a regime.
In the dart frog hobby we use Paprika and Naturose to bring out oranges, yellows, and reds.
But you can get an all-in-one supplement made by Allen Repashy, the same guy who makes Crested Gecko Diet. It's called SuperPig and it has Astaxanthin and Zeaxanthin (the polyphenols that enhance coloration, first used in fish, then frogs, now other reptiles).
Starting immediately and dusting lightly at every feeding WILL help bring out colors. I did a test on my leucomelas frogs before jumping into it and I'm amazed at the difference in the deep, rich orange color compared to the 'captive bred' look of washed out and pale orange.
Also, I am of the opinion that light intensity reallly helps. UVB bulbs have mostly blue and violet wavelengths, but if you use a combination of bulbs to provide a bright spectrum of light then that will help bring out the greens much more.
A good combo would be a UV light, a UVB light (both linear), an incandescent or metal hallide heat light, and a 'grow light' used for plants. Just make sure you use low wattages so it doesn't get too hot, but a higher wattage on the heat light will provide more brightness and heat.