How can I change the colour of the a selection tracks?
And also how can I change the colour of the background?
I see several colour palettes but if I change the colour there, nothing changes in my board.
the color of the current selection is changed in the inspector to the right.
Depending on the type of element either the fill and/or stroke color can be edited.
You can also read more about this functionality in the The Side Bar and Element Properties sections in the manual
(accessible via the Help > RailModeller Pro Help menu command).
In addition the recently introduced functionality to automatically colorize the entire layout based on simple rules such as the type of element or product number is accessible via File > Auto Colorize Layout.