Yesterday I painted a bakery case in watercolor. (Link to YouTube)
The challenge was to paint the pastries seen through the glass as well as the reflection of the skylights.
This is difficult because the brain can't see these two overlapping realms at the same time. The camera does it more easily because it's monocular.
At the pencil stage I laid out the perspective and also the shapes of the reflection areas. Within the area of each light reflection, I raised the values to a higher tint. Since it was transparent watercolor, I had to do this without resorting to opaque gouache.
Thanks to Heather and the Fresh 'n' Easy Café in Kingston, New York