Here's a weird one. I've noticed over the last couple months that my mid-2014 rMBP has slight pinstripes in colors - they show up prevalently in blues, yellows, and oranges, but are present in any color that is brighter/richer or more saturated. They aren't visible in grays, light blues, etc. Could this be a graphics card issue? It's hard to get a picture because my iPhone has a hard time focusing on the screen, but you can see it in the blue featured star.