It took me a few trial-and-error sessions to figure out how to layer colours on and under acyrlic so I thought that I'd do a really quick run-through for you.
When you're layering paper on paper, it's pretty self explanatory - the bottom, large mat first, the next smaller one on top, the next smaller and the next smaller - in that order. Easy, right?
Layer like this:

to make this:
When you're layering on acrylic, you can also do it that way - put the layers from largest to smallest on top of the acrylic, but that doesn't really take advantage of the beauty and the clarity of the acrylic. There is another way that both adds to the layers you can use and also takes advantage of the acrylic. You can layer things underneath the acrylic layering from smallest to largest.
In this example, I first put the smaller green circle underneath the acrylic, then glued on the blue under that, then the orange, and then the largest scalloped blue circle. From a distance it may look the same as the first example, but it has a distinct difference: it leaves the entire top of the acrylic free for more layers or extra embellishments like brads.
Start under the acrylic with the layer you want to show most prominently when you're finished:

Add additional layers behind this first smallest layer.

Then, on top of the acrylic, you can add additional layers, or embellishments like this large brad:
This same principle of layering from top to bottom instead of bottom to top, also can apply to other mediums such as paint. In this next example, I used 4 different colours of paint. I wanted the black dots most prominent so I put them on first (underneath the acrylic). When they were dry, I added green. When green was dry, I added pink. And, finally, when the pink dots were dry, I covered the whole back in white....finishing it, and allowing all the other layers to pop against the backdrop.
Here is one more example of this layering technique that involves stamping. For this sun, I stamped the image with StazOn ink on the top of the acrylic ATC and painted the image from the back. I started first with the pink mouth and cheeks. When that was dry, I added the yellow to the sun, and when that was dry, I painted the entire background (still underneath the acrylic) with a sky blue.
Thanks for stopping by :)
Cathy