This has been requested before, and as I understand it, it's impossible to implement, because the contents of the minimap are rendered without 'consulting' the addon-API.
The 'solution' I suggested to the previous requester:
Use a minimap-addon like Squeenix or Chinchilla to move your minimap to a more prominent location, for example, the bottom-center of the screen, where you tend to look more often.
Another option is to just leave tracking off unless you're gathering, and when you do decide to go on a gathering run, use Routes (you can find it on files.wowace.com).
I've found that my gathering of materials has increased in efficiency exponentially since I started doing things that way. Every once in a while, I just decide to stop questing and go on a materials run, at which point I check WoWHead to find out which zone(s) have the most of which materials I need, then I use Routes (with GatherMate's database, pulled from WoWHead) to plan the most efficient path to use.