Out of curiosity, I installed Myth 2 with all the project magma patches and TFL addons that I'm aware of (not the HD pack or whatever) to check out how the maps look, and it's definitely fixed in OpenGL now:
Unfortunately I still have a few minor quibbles - the flavour text for warriors actually uses one of the Myth 2 versions (Mauriac and the victory over Balor) and the blood effects are still closer to Myth 2, with a sort of "spurt" rather than a "splatter". Regular players won't notice this but it meant that Myth TFL looked a bit gorier, with blood more spread out rather than all hitting the same little spot next to the entity.
I'm not sure whether to continue using 1.5 (more faithful to Myth TFL, but ugly maps) or switch to Myth 2 TFL (small differences but proper colour maps). Even if I could fix the weird interface/cursor bug in 1.3, it'd be in 4:3, which I've used for a lot of previous videos and I think it's worth using widescreen for Myth. If 1.5 had fixed colour maps, it would be almost perfect for me