With each iteration of Illustrator, I'm finding the guidelines fainter, thinner and generally harder to see. I'm speaking of the guides dragged from the ruler or created via Cmd-5. I've tweaked the lines vs dots in Preferences, as well as their colour without any joy. After trying to use what turned out to be a stray hair on the monitor as a guide, I decided I needed to see if an actual solution to make these suckers pop again existed.
2Is it possible that the problem is the resolution of your monitor? I mean a 17 inch 4 k monitor has pretty small pixels to begin with.– joojaaSep 25, 2019 at 17:06
I mean a one pixel line in a 100 dpi monitor is about 9 times brighter than as the sameline on a 300 dpi monitor. Food for thought.– joojaaSep 25, 2019 at 17:12
2I don't think there are any options other than what the application preferences provide.– ScottSep 25, 2019 at 17:24
The monitor thought is an interesting one, but I've gone thru these upgrades of Illustrator using this same monitor. The older Illustrators and their guides just didn't have me reaching for a magnifying glass.– BlazeSep 25, 2019 at 19:20
It would be really nice to see a screenshot of what you consider "thinner" guides.
I just had a look at the guides in Illustrator CS6 and they have a thickness of 1 px. In Illustrator CC it's the same. (My GPU isn't compatible with Adobe CC so I'm using CPU rendering.)
Since guides can't be narrower than 1 px, it's must be something else bothering you. I suspect it might be the GPU rendering that's causing smoothing of the guides (though I'm not sure).
You can try to turn off GPU rendering by entering Edit > Preferences > Performance and unticking GPU Performance.
I find a straight 0=R, 255=G, 0=B pops pretty well, or I'll switch for a given document to a bright purple if the green is lost on that design, though the old-school cyan is most often OK with me too.
In Affinity Designer, they use a darker hue that still pretty close to cyan - works well too.
Hope that helps.