Firstly, I am aware that Dday’s mandate is to improve visuals and hence has made some slight visual alterations to the games and bug fixes along those lines (i.e making the Zombie Man and Cyber Demons attack states full bright, when they weren’t in Vanilla Doom, to match all the other bad guys in the game).
Something that has always bothered me in Dday is the lack of COLORMAP support in regards to Heretic.
HeXen also made some use of the COLORMAP lump. But I have yet to compare Vanilla HeXen's appearance to Dday quite as closely as I have Vanilla Heretic, but I don’t think it used this feature of the lump anywhere near as much, due to HeXen being a much darker coloured game.
Doom, made no obvious use of the COLORMAP beyond distance shading.
Dday makes some mobj's full bright in Heretic, that weren’t in the original game, both to cover the lack of support for the original COLORMAP lump and to add dynamic lights to some mobjs; Dday has no proper way to attach dlights to non-full bright states beyond a kludge flag used for the barrel in Doom.
Some mobjs that are full bright in Dday, but aren't in Vanilla Heretic include:
In Vanilla, the Orb's and Runes rely on the COLORMAP lump to make them appear a little brighter than their surroundings. The Serpent Torch has no such effect in Vanilla, inspite of the Wall Torch with a similar size flame, being full bright. So that one may be considered a ‘bug fix’ on Dday’s part, but I’m not sure that the alterations to the other mobjs were and were instead cover for lack of COLORMAP lump support.
Many mobjs and textures in Vanilla Heretic also used the COLORMAP to make some of their pixels a little brighter than the surroundings, a form of 'brightmap with distance shading' if you will. Dday loses these. Some notable examples of things in Heretic that use the COLORMAP in this way include:
The MOSIAC range of textures (used on E3); in Vanilla Heretic they gleam, while in Dday they are dull.
The Gargoyles mouth, eyes and hands light up during an attack.
The Ring of Invicibility's flashing gem.
The gleam on the Quartz flask glass.
The lighting on D'sparil's staff when he raises it to attack.
Certinally though, some of these pixels may be lost or blurred due to OpenGL.
While I have yet to look at HeXen very closely with regards to the COLORMAP, I would like to point out what seems to be a mistake regarding full bright sprites in HeXen.
The ghosts that spawn from the Wraithverge missile are full bright in Dday, when they aren’t in Vanilla HeXen. The actual Wraithverge missile is full bright in Vanilla HeXen though.
Another reason I think this one may have been done by mistake, is because the identical ghosts released from Korax’s corpse when he dies, aren’t full bright in Dday.
To get to the point of this and I may be far overstepping my place, but I'd like to put forward the suggestion that full support for the Vanilla games visual features, COLORMAP support, TINTTAB support (Heretic and Hexen’s method of transparency, that also alters the colours behind the mobj rather than just making the mobj transparent as Dday does), Spectre Fuzz and the existing visual features be enhanced (allow dlights to be freely added to any state) be added before Deng Team start adding all the admittedly stunning new visual features planned for Dday 2.