Increase the contrast of the icons
Description
For many of the grey-on-white icons, they grey should be a much darker shade; it's quite illegible and hard to spot. Point in case, one of my co workers had trouble spotting the "jump to next unresolved discussion," when I told him that they exist. Take a look at this:
That shade of grey is only a few JNDs above the white, which makes it really hard to spot and read.
Proposal
Simply darken the shade by a bit. I would prefer also for it to have a splash of colour, like the green checkmark does. That would help with visibility a lot.
Links / references
https://www.wired.com/2016/10/how-the-web-became-unreadable/
Use cases
Not all monitors have the same colour profile, gamuts, whitepoints, etc. So it's possible that this was more visible on another monitor, but was very hard to discern on mine and my coworker's monitor. Also depending upon the monitor type, viewing angle can play a role in how JND the grey and white are.