There seem to be 4 layers of skin which control the chams colors. The epidermis, which is transparent skin made up of keratin, like our fingernails, and which gets shed. Then the chromatophore layer, containing yellow and red pigment cells. Then the melanophore layer containing melanin, with brownish black and reds, and blues. And then the nether layer which only reflects white. The color cells expand and shrink, producing the various colors we see on the surface. Many cham species have bits of white in their standard coloration. It mimics the bits of light seen when the filtered sun reflects off leaves and petals.
Certain chams will show white regions in response to overheating, extreme stress, or illness.
Your Sambava does show more white than ours does, but yours is younger. My male Sambava has the white lateral stripes (or blotches) and the white "clown" lips (a defense mechanism making him look like he has huge white teeth). Yours looks like he is either starting a shed, or just has more white in his coloration. May just be his youth (not quite come into his colors yet).
What are the temps in his enclosure?