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.

As Sita Mata adorned herself, she applied sindoor to her forehead. Inquisitive Hanuman observed this action and asked her the reason for doing so. She smiled and replied that by applying sindoor, she ensured a long life for her husband Shri Ram.

The more sindoor she applied, the longer Shri Ram's life would be.
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.

Shri Ram and Sita Mata saw that Hanuman was completly covered in sindoor from head to toe and was curious as to know why.
Hanumanji related his conversation with Sita Mata and thought that if a little pinch of sindoor could do so much for his Swamy,

imagine the protection if Hanuman covered his entire body with it.

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.