I'm pretty sure I have done this before, but it's a while ago:
I have created a pie_chart ("Donut-Design", a 3D ring) with two custom_colours and two optional dimensions - meaning I can have the data shown by just one or both dimensions.
When I have one already active and activate the other one, one more ring is added around the first, the first ring shrinking.
<=> The thing is, there is only one expression, so the colours remain the same.
