The red on those uniforms! The color correction has always been the main thing I looked forward to in these HD remasters. Where TOS looked nicely saturated, TNG felt flat and video-like. It's nice to see the show with proper color timing.
See, I'm actually very impressed with the color upgrades and the vibrancy of the uniforms, but the actual uniforms are a much deeper, almost a purple-ish burgundy, so the remastering is actually changing that. It's always been the case that the red uniforms looked different when filmed (similar to the TOS gold/green uniform) but the remastering has made it even more different.
As an aside, this is such a problem that often times when the uniforms are replicated the blue and gold use what used originally, but the red uses a color that's adjusted to reflect what's seen on screen rather than what was used on set.