I do not know with what build this changed, but actually all floating windows use the toolbar color as background color.
This behaviour is not consistent, it should have the same color as the default background (by default) or should be able to set.
Please turn off the transparency via View > Themes > Background grid and transparency to achieve what you wish.
It is a bit better when shading alternate rows, but it looks nicer when TM, Glossary, unchecked segments and segment editors have the same background color (question of habits).
Might be a better idea to set a different toolbar color.
> Might be a better idea to set a different toolbar color.
See View > Colors > Toolbar colors.