I've used .9mm Pentel refillable pencils for years. They are (or at least were when I was purchasing them, yellow). The .5 and .7 mm ones were different color.
There must be a dozen of these pencils hanging around here. It never occurred to me to use them for marking... DUH.
Thank you for coming up with these ideas for those of us whose minds are on vacation .. somewhere. Joyce in Delaware