Here's a theme that I've spent far too long tinkering (procrastinating) with:
edit: I've changed it to be super minimal
no outlines
no event lines (I don't believe i've ever looked at these)
no object|event separators
muted clutter
also check out the customized top bar, get rid of the ribbon and maximize your screen space
You're a pro now, son
right click > save as > ...\Program Files\Construct 2\themes
https://dl.dropboxusercontent.com/u/53374990/Misc%20C2/GCB%20Dark%20Minimal.xml
close and re-open event sheets to see changes
I use it with 'Visual studio 2012 Dark' UI style