In event sheets, you can add comments (press Q on keyboard), and these comments can be coloured, both the text and the background, which might be helpful for you?
That link is a very old link for Construct 2!
I already know about the comments.
But what I say is something more elaborate.
An idea would be: pressing the numbers on the keyboard assigns a color to a row, for example I assign "1" color "red" to condition 10 row 5. and then I assign "1" color "red" to condition 15 row 4.
And then I should be able to scroll between the 2 or more "1"s with the keyboard by pressing 1+ctrl to scroll forward or 1+shift to scroll back.
Similar to bookmarks, but sometimes these are annoying too, they could be improved. For example, if you assign a total of 5 bookmarks to "event sheet1" and another 10 to "event sheet2" but at different times, when you scroll forward/backward in "event sheet1" you find yourself in "event sheet2", while you are working only in " event sheet1". something annoying.
You can open the bookmarks bar and select from there, but it would be nice to put the option to view only the current event sheet in the bookmarks bar.
Basically I want to say that there are many improvements that can be made, and I don't see why not.
As your project grows you need more organization.
Easing and helping the eyes is also a good thing.