We see in almost all Hanuman temples that the idol of Hanumanji covered or coated with orange colour sindoor. What is the legend associated with applying sindoor to Hanuman and what is the importance of sindoor in Hanuman puja? Here you can know it.
One day Sita mata was wearing a red powder in the parting of her hair. Curiously Hanuman asked mata, what the red powder that she was wearing. Sita mata replied “Hanuman! This is sindoor. Sindoor makes Lord Ram happy and would bless him with longer and prosperous life.”
Listening to this Hanuman disappeared from the place. Hanuman came back with red body fully covered with sindoor. He covered all his body, even his clothes and hair with sindoor to make Lord Ram more happy and even better happy life. Lord Rama saw Hanuman covered with sindoor and asked the reason. He told the whole incident and why he applied sindoor on his body.
Thus, Lord Ram gave a boon to all his devotees that those who apply sindoor to Hanuman and observe hanuman puja with sindoor would be blessed with longer and happy life.