Layers and triggers

I think your biggest problem is trying to lump layers and triggers together and figure out how they work together.

Think of yourself as the operator of an overhead projector, alongside someone giving a sales presentation. When she says, "Show the  other color.", you slide a transparent sheet over what is on the projector. It covers all or part of what is there, but in a different color. you can slide it back and forth (at her command), and show various options.

What she tells you to do represents the triggers (actions), which are completely independent of the layers (transparent sheets you slide back and forth). Other action she gives you might be "Hold up the cow", or "Turn off the projector."

The real problem I see is that of making things visible. In addition to Dave's suggestion (probably the best option), I have added some other variations. In the attached sample, Layers 1 and 3 feature hovering, while layer 2 uses a click on the picture.