Shri Hanuman, the cosmic form of energy, strength, intellect and devotion is always seen adorned with sindoor all his body.
But, behind this sindoori colour is a beautiful story which depicts the devotion of Hanuman for Shri Ram.

Devoted Hanuman was excited to hear this. Because of his love for Shri Ram, he immediately went forward and smeared his entire body with sindoor, in an effort to ensure Rama’s immortality.
Hanumanji related his conversation with Sita Mata and thought that if a little pinch of sindoor could do so much for his Swamy,
Sita Mata, moved by the gesture, explained to Hanuman that applying sindoor was a tradition for married women. Shri Ram, too, was deeply touched by his bhakta's devotion.