I found a solution that works for both my radio and slider components here:
Seems you can only drag the slider if you start at the middle, but the reason the colour clicks weren’t showing up (despite working) is that the routine was ending on the click (i.e. before the marker showed up). The code in the post above solved the issue for me so I hope it does for you too! Now I just need to figure out how to allow dragging from any position on the slider…