If you want the light to look like strong morning sun, I suggest making it less yellow. Strong sunlight tends to bleach the colors.
You may want to try a cool color of light combined with a warm shadow color. It usually works in paintings, may not give the same result in 3D... The way it is now looks more like afternoon. Just my opinion.

Also try introducing color variations in the wall rather than having solid color: greenish where some water may have accumulated in the past, closer to white where the paint has been scratched or simply bleached by many years in the sun, some rust stains from the pipe, etc.
I can tell you that one huge breakthrough I had in traditional arts was when I finally convinced myself that something I thought was a single color actually looked much better when other colors were added to it. Hope it makes sense. These are concepts from traditional arts, I am by no means a 3D expert.