Although the exact colour of the seal is still open to interpretation, there's an interesting theory I read concerning its nature. It sort of ties into what some of you have mentioned regarding the significance of the colour white. The difference between Sakura and Tsunade is that for the latter, with her genetic affiliations to the Senju Clan (who inherited the body and physical energy of the Sage), would be predisposed to Yang. As we know, Sakura was originally a genjutsu type who excelled academically and was well regarded for her intelligence. This would strongly imply that she's Yin dominant.
Where am I going with this? Well it could be that the the two seals are of a different essence. One is Yin and one is Yang. It would coincide with some of your theories regarding the colour. How this discrepancy alters the effects of the two seals is unknown at the moment though (if it even exists). Even if nothing comes of this at least it offers something to think about.
If you're curious about the source then I'll quote their post. I cited it before but I think this would be a more appropriate topic for it since the discussion seems to be focused on seals.
http://narutobase.ne...t=422666&page=2
Yin + Yang = Spiritual + Physical Energy = Chakra production.
Tsunade is partially Senju, this mean, Yang Dominant.
Yin Seal + Yang Bloodline = Chakra pool expansion + Higher Chakra Quality.
This effect was exclusive to Tsunade who had the Senju/Uzumaki Kekkei Genkai in her blood.
Sakura's effect will be way different since Sakura is not Senju, for starters. Sakura's abilities reveals that she excels in Genjutsu, revealing that Sakura is in fact Yin dominant. The Seal she developed is White, and under Taoism, White = Light = Yang.
Sakura's Seal is the contrary to Tsunade's Seal, it's a Yang Seal.
Yang Seal + Yin Bloodline = Chakra pool expansion + Lifeforce
Edited by Atheck, 05 September 2013 - 04:40 AM.