Tobirama headcannon: that he fights with his white shoulder and neck fur pelt to hide his delicate pale neck and throat. Which have taken far too much abuse in his shinobi career.
The tactical black turtleneck is there for similar reasons in casual settings.
He also is doing everything possible in battle to appear as big and as broad as his anija. Like a cat puffing up their furs to seem more threatening. Because if you look really close, and Madara DOES, you can really notice the build and size difference between the two massive senju brothers.
Madatobi headcannon: (established intimacy setting) Madara absolutely takes advantage of both the sensitivity, the mortal fear and the clothing and pelt coverage to completely demolish Tobirama's pale soft neck with bruises and bites and kisses. He takes extra time to make sure every inch of skin is as ruined is it can be before he moves on to the throat. Which he can attack creatively from the inside with ...other bodily parts.
If Tobirama sounds horse the neck day then maybe he should stop working so hard? Take a break! Relax. Go to the hotsprings maybe? Madara suggests the next day, in front of everyone in the council meeting. Tobirama just glares harder, glaring at the reason he cannot be seen without layers for the next week or so.
Later on that week, Madara constructs his own little private onsen hidden in the mountains and tricks Tobirama into meeting him at the location, making him provide the water with suiton, and then Madara heats it with katon. They relax together. Madara makes more marks that will take longer to heal. On purpose.
