Welcome to TVPaint Community forums !

I've been working in TVPaint today and just now hit a keyboard shortcut that turned all of the thumbnails in the clip I am working on to black. What keyboard short cut did I hit and how can I get the thumbnails back.

I've tried to attach screenshots from the clip timeline

first screenshot shows the clip with the black thumbnails the second show another clip from the project that has normal thumbnails.

Perhaps you hit "Shift-B"(chenge Background mode).

..and if so, you just need to hit Shift B again to get a transparent background, and yet again to get back to your white background colour, one should maybe add.