I'm using the brake-in slides so they cover various shades of basic colours including white, grey, red, green and blue.
It's interesting though that you said that the effect is less obvious when you first power up as that's when I checked it with the slides. I'll have to do that again once it's warmed up for a while. I wonder if it's related to the panel over heating or something along that line.
Again, in my case the effect is very subtle but, apparently, noticeable in very specific circumstances. If it doesn't worsen I'm not concerned. I just wish my wife hadn't pointed it out to me because I would likely have never picked up on it otherwise.