Thanks for sharing your work!
(and welcome to the forum)
- "IconColourOverride.Default" is overriding the colour of the chekmarks in the menus.
- If the Track Information is selected in the now playing bar at the bottom panel, I have no idea how to change the font colour.
- I don't know how I could test the three "Controls.ProgressBar" elements or where I find them in Musikbee.
1. If you want to override the checkmark, you need to use a 16x16px image file, encode it to base64, and copy it in your skin.xml under 'images' as <element id="CheckTick">
(a forum search should lead you to how that can be done)
You will probably also want to define others such as "CheckTickDisabled", and "LargeTick". (for the Panel Configuration panel)
2. Over the years, the functionality of that panel has changed a little bit, and I am not completely sure how it is controlled at the moment, but far as I know the text colour is auto-generated depending on the background colour.
3. These are obsolete (as far as I know)
If you check the paragraph at line #10 of my sample skin you can read my current understanding/handling of those.