You can jerry-rig a tagging system that shows in all (individual, family, family group sheet, pedigree) views fairly well, except for list view. In the list view you have to tick the thumbnail link on each individual link to view it.
1) Upload a picture of a solid color block,(your choice and there are millions on the internet), to one of your "completed" individual records. It must be made the primary picture for this person. You should cut down the size of the color pic file to the bare minimum before uploading to your tree.
2) You can now attach the same color block picture to every completed individual record, it always has to be the primary picture for each individual.
3) If you're really into color coding you can set up a whole system, specific to whatever you need. Go crazy.