IF function with Conditional Formatting

First off, this is my first actual post here, but I've found very helpful information in the past, so thanks to many of you for help previously given!
Now for my question...I have a schedule for my personnel. When picking their work and off days, there can only be 50% off on any given day, and only 25% off on special days and holidays. I already have the formulas in place to add the numbers and to alert me when there is an excess above 50% off. I have created an additional column("Special") that I'd like to use for the special days when only 25% can be off. I want to be able to enter "y" in this column, then have it change the formula to figure percentage and to turn red when it exceeds 25%. I have included a working copy of the roster for anyone who may be able to help.
Thanks in advance!
Garrett