With the high contrast setting "contrast white", the highlight color is purple an the Text white:

The buttons in Kleo do not honor this, e.g.:

The button on the left has a lighter purple because it's background color is fading in and out.
I suspect it is no good idea to have the pre-selected buttons change background color this way as the text color needs to change in this case, too.
The pre-selected Windows explorer buttons do not do this, they are simply purple with white text.