While working with transparent colors, I noticed the peculiar issue that when flattening transparency, the color changes quite noticeably.
I'm in CMYK colorspace, and I have below two shapes with the same basic CMYK red color, but the left shape is at 35% opacity.
After flattening transparency or rasterizing with white background, this is the result: Interestingly, when I place a white shape behind the transparent one, it starts to look more like the flattened image.
This leads to the strange conclusion that the white artboard isn't really white? Why do transparent colors render differently on an artboard and on a white background?
UPDATE: This might be a bit irrelevant, but to add to the mystery, after turning on Simulate Colored Paper in Document Setup, and inserting the screenshots used here into the document, they seem to become transparent outside the artboard! And turning on Overprint Preview does not help.