It's the same on my GR iii, and I never paid attention to it much because this is how my computer also renders high resolution images(looking at you, k1 photos
). It only takes a second at most, and the image doesn't overall change color or anything. It's more noticeable for finer detail.
I'm guessing it's to show something approximate faster and then refine it, so you don't wait to get a sense of what you're looking at. The back screen has a much lower pixel count than the captured image (in general, different), and so it needs to be adapted (downsized) for display.