The Hulu Brothers correspond to the color scheme of the rainbow. In Sanwa's case, he represents yellow.
If you find 2 Lens in the Abandoned Mine it will start a quest to bring it to the research center. Complete the quest to get color blind correcting glasses. Go find Sanwa, give him the glasses and convince him to open his Barber Shop again. You will gain friendship with Sanwa AND +10 friendship with the whole town.
To give him his glasses, you need to have them selected and go talk to him. You'll need to tell him to 'man up' and he will wear them.