Multi color guides.
I use templates with several close guides. When zoomed in its sometimes difficult to tell which guide I'm at. If the Make Guides selection could have an additional drop down with a choice of 3 or 4 colors, if would help prevent mistakes.
Henry Tregenza commented
This would be so useful for groups and layers!
Agreed! Could do with this!
E. S. Rigby commented
This would be a really useful feature for commercial design work. I do a lot of design for panel art and silkscreening on metalwork, and the artwork has to be precisely aligned with edges, holes, degrees of rotation of potentiometers, etc. It can get really messy if there's a lot of features to deal with. If I'm zoomed in close, or there's two guides very close together, I can lose track of which one is which.
If ruler colours could be individually defined or coloured by layer that would be extremely useful and provide a much tidier and more readable workspace.