Let's improve the Curves by adding RGB buttons to switch between the channels!
Now, with the drop-down list, we have to click twice - first time to activate the list, second time to choose the channel. Buttons would speed up the workflow. 🙂

That's what we've already got in ACR.

Showing the opposite colors is also a good idea, by the way.
But it could be optional - some experienced users may find it distracting.