Excellent! For educational purposes you can try increasing the Mask Size to 2 or even try the 4K Optimized version @ 1080p.
Although the preset is usable now, it’s still not quite finished as I still have to fine tune the brightness and gamma settings and do some more testing. I didn’t bother to revert because I changed those settings (which broke the presets) for good reason.
Before I was doing a lot of manual “hacking” in order to get the colours to look right and that led to many inconsistencies and possible clipping of the colours.
My computer monitor presets are my original Dreamcast presets that looked good so I was surprised when you said you had a problem with the colours and that my Ultimate Virtual Slot Mask was the best, because while it could be better or even the best, that’s the new kid on the block and Dreamcast had been “solved” a long time ago by my older presets.