Border colour for viewing pane and viewer?

I've found the option to change the border colour for thumbnails in the folder views, but I can't find a similar option for border colour when viewing pictures in the viewing pane and the viewer. Just standard white. I've found the option to turn the frames on and off, and the background colours, but no border colour option?

Apologies in advance if I'm being thick and it's really obvious!

There isn't one currently. The frame around images (if turned on) is always white.

Could the customisation option possibly be added, please? It would then match the thumbnails and give a consistent look.

We'll put it on the list!