I have noticed that using black outlines makes the selected area pop out more, with some exceptions, like shadows and background scenery. I have also noticed that the perceived colours are different. It only has a slight difference, but it can make a massive difference between, getting a theme across and not getting it across.
By adding a black outline outline instead of a dark brown one, it makes the colours seem lighter than they are.
If I add back in the shade I removed for more shading, it creates a darker shade than without the extra shade, but still lighter than having no black outlines.
The screenshots I am showing are of the flute animation in development.
All the analysis in this blog post could just be, because of my screen contrast and brightness, so my analysis could be incorrect.
Game Growth 