Thanks for the tip, I'll certainly keep this :)

The low contrast makes it difficult to make out the traffic light, it blends into the building.

In addition, the colours look very dull because the shadows are just darker versions of the base colours. In reality, shadows often have a different hue because the ambient light in an environment is rarely pure white - the colours of objects bounce around. In artwork, it's often effective to shift all the shadows towards some hue to both make the colours more interesting, and to give the scene a more unified look.