Since it's Autumn right now I've been trying to paint some yellow trees! I'm finding it difficult to capture the brightness of the yellow leaves with the blue sky underneath. Are there some technical tricks that I'm missing, like should I be using a more opaque yellow paint? Should I use a different pigment in the sky?

A follow up question is what kind of shadow color works best for yellow leaves? In this example I just used an orange, burnt sienna.

This sketch was done with Daniel Smith paints: Ultramarine Blue in the sky, neutralized with Goethite (which is similar to raw sienna). Leaves are Hansa Yellow Medium with Burnt Sienna for shadow color.