On HDMI output, black is grey

cde1

This is not UP's fault, but rather a long known problem with open-source Intel Linux drivers that goes back to Sandy/Ivy and that Intel never fixed. Basically when connected to HDMI, the driver assumes that a TV is connected and arbitrarily restricts the RGB color space to 16-235 instead of 0-255, leading to faded colors and grayish black on a normal monitor.

There is fortunately an easy fix: simply run:

xrandr --output HDMI1 --set "Broadcast RGB" "Full"

To make it automatic at login, a simple autostart shell script can be created. On XFCE, use Settings->Sessions and Startup->Application Autostart.