Currently we can modify UDL XML file for matching with dark theme by adding colorStyle="0" in DEFAULT style:

<WordsStyle name="DEFAULT" fgColor="DCDCCC" bgColor="3F3F3F" colorStyle="0" fontName="" fontStyle="0" nesting="0" />

and colorStyle="1" in other styles:

<WordsStyle name="LINE COMMENTS" fgColor="FF8040" bgColor="3F3F3F" colorStyle="1" fontName="" fontStyle="1" nesting="0" />

for ignoring the style's background color and use dark theme's one.

It will be good that users can set colorStyle directly via UDL dialog's UI.