Frankly, would it be before WinVista - i'd also request window captions haveing different, non-system colours. In Windows 95-2000 timeframe it was a popular way too decorate your app :-)
For "your app", who hold you back to do a simple borderless form with a selfmade caption the way of how you like it?
Well, two reasons.
1) there was a Delphi component of extended caption, to just drop on the form. In RxLib/JVCL, maybe the code is still somewhere there in CCR
2) Windows GDI separates methods (messages) of painting caption and caption behavior. Full-custom mode would give you burden to replicate all the behavior, including animations, that are user-customizeable at that. So, overriding painting of the caption and nothing else was better both by concept and practice.give the gutter of the source editor different colors
To me the most annoying problem was hitting F7/F8/F9 in the wrong IDE. So i did not even look to the source editor.
I was thinking into making non-standard background or fonts too, BTW, but i feel reluctant to do so. The IDE for tests/pataches should be as vanilla as possible, and that would mean i have to make "non-standard" colouring for my main IDE.
Ok, IOW, there is no already existing functionality that my ignorance missed.
I wonder, though, if some customization of main form from "lazarus.cfg" gets implemented, would it be immediately frown upon as violating Lazarus purity and putitn unneeded complexity upon mantainers.