The slightly different colors and hues come from the stabilizer used in the manufacturing process. This chemical has a fairly wide color window (20aspa to 150aspa). Mercury typically sees around a 30aspa to 50aspa, which for the most part would be colorless, the spec or tolerance can go as high as 150aspa, which would still be in spec and be a slight amber color. UV light can also have an effect on the stabilizer, causing an oxidation of the stabilizer, which would increase the aspa spec for that particular bottle.
Note that his color difference or oxidation of the stabilizer has no effect on the stability or the performance of the product. Mercury has performed accelerated and real time testing on all Mercury products to the point of actually exposing them to enough UV light to oxidize them to the point of turning brown with no loss in tensile strength, set times, or increase in viscosity.