Hi everybody. I had a similar problem with my Series 2 Aluminium. It looked like the oleophobic coating was discoloured and i had a vertical yellowish strip on the left side of the Display while the rest of the Display seemed to have a blue/violet gleam in certain perspectives. How did the discoloured coating look on your watch? Apple replaced my watch as well. I thought it was an manufactoring defect. But know i wonder if it could be caused by clothes softener or something else and the replacement will suffer from the same defect.
Mine looks like brownish rusty smudges.