Dementus parachute cape going from white in the beginning like a ‘saviour’ to covered with red paint once he meets a war boy and darker towards the end of the film has a GRIP ON ME. I’m torn as I think it could relate to two things.
1) how his followers see him as a saviour figure, and how active he is to use them as cannon fodder/ no true loyalty or freedom he pretends to uphold in order to gain followers. (See the Citadel Speech)
We all know Dementus is a manipulative prick the first time he ever meets Furiosa however, would be able to hide his true intentions to any child that wasn’t trained/like Furiosa. Taking the best care of her and saying he was going to take her home if she gave him directions seeming as if he was a good man when he did this in order to find, destroy and parasite off of the green place. His followers at this time see him as a saviour maybe not to the effect of immortan Joe but they see hope in finding a ‘better land/resources’ (See beginning of the film/ fruit tent scene)
It first becomes muddied when he encounters his first war boy (not after he commits his first act of violence!)This scene is later followed by his Citadel speech scene and follows his followers getting fucking blown to pieces by his arrogance and he doesn’t even try to save them. He only goes after Furiosa and the poor man who’s his walking dictionary only to further his own needs. His followers see him less as a saviour and the gang starts to split between leaders (see gas farm decoy scene that follows this, where there is tension between gang leaders AND he starts shooting his own men for decoy). (Also the Citadel I just mentioned)
And then lastly we see it towards the late second to third act of the film once he is separated from Furiosa where the top of the cape has gone black almost like it is covered blood. This is when he acquires gas farm and bullet farm (the black could also represent tar and the fossil fuels of both plants/greed). However this is when he is at his most volatile, his own people in the respected farms are planning a district 8 style uprising and he can’t keep his own gangs together due to his reckless behaviour. This is also best shown in the final act when he uses two out of four of them to be literal decoys for him so he can escape with his life. His followers no longer see him as a saviour and he has only has core followers left.