The blue comes from RA's logo. They basically use shades of blue and yellow in equal amounts across the site so I don't know, either seems correct.
Not sure if it is Ubisoft that should be changed considering they seem to have moved away from the blue now, only certain buttons still use it, entire launcher is more white on black now.
But as I mentioned in another thread before, I think the best path forward is just to allow customization of the colors that would be specific to each account. Inevitably as we add more services, there's going to be more color similarities and that way users can configure them based on the ones they have linked. Since someone that doesn't have Ubisoft linked might not mind that RA is blue, for example.