What makes a tree frog red? And how is it that some animals can be blue?

Question

For example some monkeys have blue on their faces.

Answer 1

do you mean why are their eyes red?
One reason the eyes are red is because they are noctornal. the red helps them see.

The Red-eyed tree frog can change its color with its mood from a darker green to a reddish-brown. This is also a form of protection from preditors that may want to eat them.

Answer 2

This question has no meaning..

It like saying..
What makes a race car have stickers? and how is it that some bikes are blue?

Animals can have any color, Some tree frogs are green, some are black, brown, blue with yellow spots etc...