Why would Henry the chameleon have blushed into deep red?

In Ruskin Bond’s story of Henry, the narrator mentions two primary reasons that the chameleon’s color changes from green, which is his customary color, to red. The first is to indicate his great anger when the narrator tickles him in the ribs. The only reason the narrator, who seems to be a child, gives for the tickling is that Henry’s passive attitude was boring. Along with turning red, the tickling makes Henry swell up in size, sit up on his hind legs, sway, and hiss. Another reason Henry turns red is apparently fear. When he turns up in a fruit basket at the school, his sudden appearance frightens the principal, Mrs. Das, who screams. Henry turns yellow first and then red.
http://goldennile.blogspot.com/2015/04/henry-chameleon.html