I bought a refurbished 13" macbook pro. I notice that if I drag a window to the bottom, the colors fade slightly (for example, the grey part of the window, as it gets toward the bottom of the screen, is a little lighter that at the top. Has anyone else experienced this?

It's a little frustrating. My lovely 24" mac was replaced because they couldn't find what was wrong with the display. But the brand new 21.5 inch has the "yellow tint" issue that I've been reading about. You think that they would fix these things. Now I have to go back to the shop -- again. This is the fifth or sixth time I've been to the apple store in the past two months.