One of the most important colors used to paint Hanuman murtis (idols), images and sculptures is red/chandana. Ever wondered why Hanuman idol is painted in red? The idols are painted red/chandana for the good of Sri Ram.
It is said that Hanuman used to observe Sita wearing a red dot on her forehead. Mata Sita used to daily smear/coat/mark the parting of her hair with vermilion powder[sindhoora].
One day a curious Hanuman asked Mata Sita, ‘Why are you smearing vermilion on your forehead and the parting of the hair?’
Sita replied, ‘It is for the good of Sri Ram.’
Hanuman, who always wanted to do something for Sri Ram, immediately took the vermilion powder and smeared it all over his body.
To a stunned Mata Sita, Hanuman said ‘If you have to wear a red dot on forehead to achieve good of Sri Ram, I need to smear my whole body with red paint to achieve the good of Sri Ram.
From that day, Hanuman’s images/idols are painted red/chandana.