In indirect painting, you use the fact that all layers of paint mix optically. This clip shows you how the painting 3C was produced from start to finish.
There are many schools of thought when it comes to painting. It is no religion. The exciting thing is that you can do anything you like. But with 100% contemporary materials, the approach here is hundreds of years old and has been used and mastered by many artists. The technique simply subscribes to the idea that paint is not just a surface. Rather it is a shimmering optical illusion that appears real because light travels through several layers of paint film, get reflected by the canvas so as to work its way back to you, whilst mixing all the layers optically as if it was glowing.
It is the glow you are going for. While it may not look totally backlit, it has something about it that cannot be achieved in just one paint layer. In any case paint is not an opaque surface, which means we might all have dabbled with the technique without knowing.
Feel free to look up the topic indirect painting method at your leisure. It is potent stuff and was the dominant way of painting until the advent of impressionism.