After pumping this morning I noticed my milk from each side is different colours. Why is this so? Is it normal?

Probably the bottle with the slightly darker coloured milk contains more hindmilk, which is usually “creamier” as it has higher fat content. It is probably also “thicker” than the other bottle with the lighter coloured one. This could happen if your baby drinks more from one side, emptying that side more thoroughly than the other. Don’t worry, the milk is still safe for consumption.