Good color contrast for editing

have you tried to draw the grid on top of the items? (Preferences -> Appearance -> Grid line Z order) And next to it you have a checkbox Show dotted grid lines. These might help. Otherwise you can try the skin from my signature. I payed special attention to this detail when making it.

A constructive suggestion: Please tell us what theme or color setting in a theme works out so far best for you. So everybody get a more precise idea where the problem is. Overall you have to consider this. Some theme devs and modders use the software in a specific way, where your needs are not considered simply because they never see it (on screen) in that way like you - different workflows...

TBH I couldn't work with that much colour going on on screen. I don't see anything, it just hurts my eyes and I have to think too much about what it can mean. But I believe I have a clue where your problem lies. :) Let's try the other way around. Please tell, what is too unclear for your on the following screenshot (I hope I included every state you wanted but maybe a example project to share would be handsome). Btw - you are not colorblind? Just asking - no offence.

I agree that you would see this different. I would like more contrast, especially for the time selection. I dont see anything wrong with you working the way you do, I would just like more contrast. Hopefully theres some magic combination that will work, or more perfectly, we will get item fill mode selection for grid and stretch marker lines