Never mind about above post!

Anyway ...
I had the same problems with UT99 being Dark when I updated to Win10 as you did David.
Doc Flay told me to add the New Direct3D renderers to my Computer, and it "cured" the problem to a degree, as it appears it did with your system and game.
I actually added a number of Direct3D renderers, higher than 9 also. (I gotta check which one I am using)
I have heard that 9 is best for UT99, as UT99 is currently.
FYI - there IS a
New UT99 patch coming Soon! - Version
469
Read More at:
https://hooksutplace.freeforums.net/thr ... ersion-469
I believe this New 469 patch will correct these sort of problems as it is supposed to Update UT99 to current systems.
Also, you said: "What I like about the GL version is that the bottom of the screen where the weapons are shown is not dark."
Could that be just the
HUD Opacity setting being set different on each renderer you tried?