Format help when not using formula

I am not familiar w/VBA. How my spreadsheet is set up, I input into 1 cell a specific date....the rest of the cells are calcuated based upon the formula used ex: =WORKDAY(AK329,-AH$18,Holidays). There are appx 27 columns and 350 rows that have this formula. At times I override the formula with a specific date and use the spreadsheet for scheduling. What I'm wanting to see is if I override the formula, the cell changes color so I can see it in a quick glance. The reason want to see at a glance, sometimes the wrong dates are entered, changed, etc...and I cannot see what has been changed to a hard date vs. using the formula. I currently do this manually, but sometimes others maintain the spreadsheet and they may not change the color. I thought there might be a conditional format for when not using a formula, as you can conditional format based on a specific formula...thought it might work the opposite way. Does this make more sense?