Two things that are showing here. One, the amount of water it is getting seems to not be enough. Even if it is being watered every day, sometimes if the soil dries into a hard ball, it doesn't really absorb that much water. I see you have rocks on the top of the soil, maybe remove those and see if the soil is actually wet. Crotons like a lot of water, I've never over-watered a Croton, nor have I ever heard of one being over-watered.
The second thing, they require very bright light. From the picture, it does not seem to be getting a lot of intense bright light. The way I know this is the leaves do not have the reds and yellows they generally have. I don't know where you are located but you could do one of two things. Every few days you could bring the whole enclosure outside (weather permitting); this will be both beneficial for the chameleon and the plant. Or, you could purchase a 6500K light to give it the bright light to give it back that color.
Chase