Even within the first two seasons londos style change is very subtle before completely changing.
In the first season we often see him wearing vibrant clothing and outfits and in his waldrobe we see many outfits brighter than the one pictured. In season two I feel like even in the beginning we see a subtle shift to more duller less bright colours. He shifts to less vibrance in the scenes which I assume it's to do with him dipping his toes into the waters dealing with Morden and while he still has many of the flair it's seems somewhat subdued. This was also around the time he started plotting with Refa who is shown to be as bad as Morden. He also give away sensitive information to Morden that killed hundreds of narn on survey.
Half way through is where we see a sudden shift as his government start war with the narn and he essentially gives his soul to the shadows and seals his fate.
He's now committed to the path the shadows have played out and is no longer even entertaining the idea that he's no longer in service of the greater good.
I am not sure if his hair is relevant at all but I noticed after season one his white strips were less pronounced in much of the later show.