One of the many ways to create glowing color in watercolor paintings is to use the technique of glazing.
Glazing takes a bit of patience as you have to allow each layer to dry before you paint the next layer, but it can create stunning results.
Here are a couple of little demonstrations of glazing - cherries and an apple.
In each of these quick studies, a layer of yellow was first put on the fruit. When that had dried, a second layer of yellow was placed where the shadows would go in order to darken that area - even though it was in yellow.
From this point, you begin to build color through layering glazes, allowing the paper to dry in between each glaze. Depending on what color you choose to put next, and then next, and so on, you will end up with a different result. The orange glow in the cherries was achieved through layers of yellow, then red. Because the white of the paper shows through the transparent paint, as well as the previous color laid down on the paper, your eye perceives the color as orange instead of red. And the orange is a vibrant glowing orange rather than a flatter orange which can result if you use an orange out of the tube. With the apple, there was no green used except for the cast shadow on the wall.
Glazing is a very fun technique which can give you surprising results. You should try it!