As others have said, control of the

1) thumbnail border width

would be nice.

My other request/question is about the image nav buttons that appear on the main image (when switched on).

1) Can the colour of the circle be changed? It's a medium grey, I'd like to change that grey. (In the same way as the background colour of the main button bar can be changed.)

2) Can the position of these buttons be changed? At the moment it seems that they're necessarily overlayed on the sides of the main image. I'd, for example, like to put them just outside the main image area.