Ok, so I just did a DDU. When using Microsoft's Basic Display Adapter, on low resolution, DP works fine. As soon as I installed Nvidia's drivers, it shit the bed while HDMI always works.
Tried a TV+Monitor setup. HDMI on TV, DP on Monitor. It will work on both but if monitor is running higher than 60Hz, won't work and like before, color is very washed. However, if I duplicate screens (instead of extending), it... works fine? Even on the same monitor. If I have HDMI and DP connected to the same GPU and same monitor, duplicating works well.
Could it be a Windows issue?