Ed;
Your answer was fine, just a little vague on the reasons.
Scott;
Your answer is backwards. If a print is too yellow, add yellow, if it is too magenta, add magenta and if it is too cyan take out magenta and yellow.
The blue sensitive emulsion forms yellow dye. If the print is yellow, you must subtract blue speed by adding yellow filtration. I know it is counter intuitive, but that is the way it works.
You were talking from the aspect of a reversal print material and were correct, but not for color negative printing.
Another way to look at this is this fact... The red layer (cyan dye forming layer) is the anchor point for speed. So, you don't want to affect the red layer by adding cyan filtration and affecting the total speed of the paper. This is another way of looking at what Ed said.
PE