In other professional CAD tools the sketcher environment displays sketched lines in different colors/hues depending on the status of constraints.

For example:

non constrained lines are shown black

Constrained lines are shown in a dark green

And a fully constrained sketch is shown in a bright/light green

This is helpful for determining if the sketch is fully configured or if there are constraints missing which could cause problems later on in the process.

Also this would make the lines more visually distinguishable from each other in the process of sketching and constraining.