Color Compensating filters

Although I've been printing in color for a while, I'm still not sure

how Color Compensating filters are used, or why they are so

expen$ive. Correct me if I'm wrong but there are three types of

filters used in color processing; Color Conversion, light balancing,

and Color Compensating filters. Now I read somewhere that you can

use Color Compensating filters(CC) in the darkroom to spot color

correct your prints. Has anybody out there tried this before and if

so how ? Color compensating filters filters come in a degree of

range values such as: CC05M Mangenta, CC10 mangenta, CC20C Cyan,

CC50Y Yellow, etc. So by applying a certain filter range to a

particular part of a print you can selectively adjust the color of

that part of a print. Meaning that if your print is totally perfect

except for the yellow teeth of the main subject, you can adjust that

by using a CC filter, but how do you do that ? Do you cut a small

piece of a very expensive gelatin filter and somehow flick it over

the yellow teeth ? or does the filter go under the enlarging lens ?

Why are these filters so damn expensive and misterious ? can

somebody please answer that for me ?

I print colour negs. A fellow printer sometimes uses a disc of magenta filter as a dodger

(i.e. stuck on a piece of thin wire). She uses it when printing portraits to lighten a face and

simultaneously remove a pink complexion. Doing teeth in this way would be tricky unless

it was a very large print, or an extreme close-up.

I've never used those gelatin filters but I do occassionally burn in with a different filtration

setting dialled into the enlarger.

I always thought the main purpose of the filters was to enable people with a black and

white enlargers to print colour (i.e. slide the filters into filter drawer, or use them below

lens). - Must be an exercise in frustration as the 5 unit increments are too large for fine

printing.