I checked the official documentation but I could not see a specific colour to use for the icons sitting in Safari's toolbar (e.g. "toolbar-icon-72").
I have tried a number of different greys and although I have the one that looks good to my eye, it may be a little off to others. So I was wondering if there was a recommended colour ?
I also tried using the bundled Digital Colour Meter in macOS to determine a single grey colour, but of course, at the pixel level, anti-aliasing leaves that very much down to interpretation.
I have gone with 141/141/141 (RGB).