Voodoo 1-3 couldn’t render 32-bit color, so maybe you were noticing the lower bit depth?
3dfx did design some tricks into the video pipeline on Voodoo 2 and 3 cards that allowed for what they called 22-but color, and it definitely looked better than other 3D accelerator cards’ 16-bit modes - but it was still not as clean looking as true 32-bit color. (Interestingly, the filtering they did was applied after the framebuffer, so screen captures would only ever show the lower quality original.)
3dfx did design some tricks into the video pipeline on Voodoo 2 and 3 cards that allowed for what they called 22-but color, and it definitely looked better than other 3D accelerator cards’ 16-bit modes - but it was still not as clean looking as true 32-bit color. (Interestingly, the filtering they did was applied after the framebuffer, so screen captures would only ever show the lower quality original.)