Any mag that protrudes is easy to identify, the AR/AK and possibly Ruger (which Ruger) is simple. The tape idea, like colored duct, etc.
If it leaves a residue that comes off w/ a little WD40 or "goof off". On the duct tape I'll sometimes use a sharpie, when I'm testing mag/ammo/follower/spring combinations. If there's amag that's consistently or repeatedly a reliability issue, I'll mark that too.
Magpuls work but are more expensive than tape.
An orange vs. green or black folower will work but only when empty and not always at immediate glnce.
The glock mags will be a little more difficult.
You can "slightly" mod. yours w/ a dremel'd dimple under the base plate and w/ a crayon or wax pencil fill the dimple, wipe the baseplate the wax will remain and stay in the dimpled recess, re-do as necessary.
Or for the Glock, grab some replacement baseplates from Pearce Grip co. and replace yours, its a non-perm. mod. that allows you to reverse the mod. They have the same dimples already integrated for this exact reason.
Hope it helps lots o' luck.
/S2