Layers will work in a more conventional way than tags.
The interface have still some way to go but the layers will have a selected layer, the current layer you draw on, the layer color, that you may pick if you want to override the shape color for visualization and of course you can hide/show.
Also this prototype will be more polished, but the reason is shown is just to see what is it about.
Add/Remove buttons will be likely down, and Add button will show a dialog where you can set the name and color.
How you define custom colors: every time is picked a random color
See more in the the next nighties for issues and how things will work.