and seeing it's apparent how I like to photograph these guys on occasion (cough), maybe the following will help explain why..maybe? (I noticed you can double click to enlarge-large it?
A chameleon’s colorful beauty is truly skin deep. Under the transparent outer skin are two cell layers that contain red and yellow pigments, or chromatophores. Below the chromatophores are cell layers that reflect blue and white light. Even deeper down is a layer of brown melanin (which gives human skin its various shades)..could you tell this photo below was just an excuse to add the Iris? So blow it up-
Levels of external light and heat, and internal chemical reactions cause these cells to expand or contract. A calm chameleon, for example, may exhibit green, because the somewhat contracted yellow cells allow blue-reflected light to pass through. An angry chameleon may exhibit yellow, because the yellow cells have fully expanded, thus blocking off all blue-reflected light from below.