I'm not sure that I am in alignment with the concept that every small change request automatically implies a need to 'chip in
Yes I totally agree, this feature seems to be a very obvious requirement specially when you take into account how many other areas contain the option for custom css. For some reason support don't see the benefit or the need of having this feature on the separator. I have asked them before if this is possible and they confirmed it is.
I use separators a lot purely to hide attributes to keep my forms uncluttered and simple, however when the separator expands there is an unnecessary border which adds to the clutter. I also use the form advanced script as opposed to a rule to expand a normally closed separator if a condition exists, all for the sake of a simple and elegant behaving UI. Being able to shade the background would also be very nice.
Maybe support can come to the party here and add this feature. Also being able to place more than one separator on a line (restrict to column) would be a very powerful feature , but that may be more complex than a simple css style
