So are you wanting to change the skin? If so, then you can probably accomplish that by modifying the layouts.
The reason why the text is dark is because your using the built in TimerWindowCreate. When you add the lotv campaign dependency you need to switch to using libVCUI_gf_TimerWindowCreate. Just take a look at the trigger GUI timers. You will notice that there are two create timer windows to pick from. Use the one that references LOTV.
Ik how to make custom UI. That's something i was gonna try but i figured i was doing something wrong. I was hoping to make the standard one work though bc i assume it's more optimal than periodically updating a custom dialog
For the timer dialog to function correctly it must be sent the appropriate animation. That is how it is used by Blizzard and why it works in Coop mode. This is a fairly commonly asked question where the specific required animation string. Specifically HighlightStop.