Madara's soulmate is a Senju. He doesn't know which one, since so many of them are painted in shades of grey. Hashirama has no colour whatsoever, anymore, but the man isn't his soulmate. They've spent far too long together, both at the river and on opposite sides of the battlefield. Butsuma is also grey but everyone knows his soulmate was killed after the birth of Itama. Tobirama, Kawarama, Itama, Touka, several Senju he doesn't know the names of, the youngest of the enemy, all are monochrome. The weapons are hard, since he doesn't know which ones are actually grey and which ones have had their colour leached.
Several Uchiha, including Madara's own brothers, have splashes of grey across hands, arms, faces. Whoever his soulmate is, they're skilled. Many Senju have grey patterning their faces in the way Madara has seen older, blind Uchiha use to 'see' their friends and family. But then the trees are grey, not near the ground but high in the branches, and a patch of grey river passed him once (he wasn't even aware that that was possible), and members of many different clans have splotches of grey, civilians, leaves, paths through forests and plains, rocks, even the odd wild animal. It's like his soulmate has been everywhere but if they really are blind, then none of that makes sense. And if they aren't, then why the face touching? Unless they picked it up from someone else when they were young which would make a small amount of sense, he supposes.
His father tells him, in no uncertain terms, that it'll be impossible for him to ever meet his soulmate on peaceable terms. Butsuma is a cruel man and it's unlikely his sons are any less manipulative and bloodthirsty. Madara bites his tongue to keep him from telling Tajima that no, Hashirama is not like his father. That would be stupid and dangerous for both Hashirama and himself. Besides, everyone know Tobirama would never support peace, never allow his Anija to make peace. Not without sabotaging the Uchiha at every turn.