The scroll wheel is simply doing the job it was intended for in and outside of Cubase.

You can quickly and easily browse the parameters in many lists and fields within a Cubase project, using the scroll wheel. This is very useful as long as you are aware of what you have last selected and what your cursor is hovering over, and therefore what any action you take may be affecting.

If your cursor is over the track color parameter, the scroll wheel will scroll through the track colors.