Add Option to the slicer to change the selected item's fill color

[VahidDM]

In Slicer visual, it isn't easy to find or see the selected items when the background is dark. It would be great if we could change the fill color of the selected item's checkbox.

[vzuckero]

This should be part of the settings like "checkbox border" or something. This is why so many customer tools get used in the product.

[RSH]

Seems useless to be able to set the background color if you can't set the foreground color. Functionality was not well thought out.