However, here the significance of geruaa is a bit different. Geruaa is generally considered a color worn by sages and hermits, and thus, here symbolizes people who have left everything to find the One they are looking for. The word geruaa in the song rang de tu mohe geruaa, thus, gives a kind of sufi touch to the it, as the lovers here want to get colored ‘geruaa' like someone who has left the worldly things, and just be in love.
Btw, the orangish color you see along with the black in the picture below, that is Gerua.
For the translation of the entire song, check THIS LINK.