Adding GUI widget simpler than a ColorEdit? (Legend for labels)

In the latest Open3D 0.13.0 [demo](https://youtu.be/rWLKxOewbxU), I saw it's using ColorEdit() as semantic labels, as shown below:

Following this, I also created something alike (a figure legend):

I checked all the GUI widget options and didn't find a better way than ColorEdit, but the only thing annoying was that the RGB values are always displayed.

Therefore, I have the following feature request:

**Describe the solution you'd like**
Ideally, Open3D can extend its GUI widgets by adding some basic plain 2D geometries (square, circle, etc.) with changable color.

**Describe alternatives you've considered**
A quick solution would be just offering a simpler version of ColorEdit(), i.e. without the RGB value displayed and maybe even without the color picker.

Thanks