Have you tried usig conditional formatting..?
To find it press "Format" - Conditional Formatting

you can set conditions where the cells in question meet a certain criteria..

"John" wrote:

I have set up a holiday planner and need to include a 10% absence allocation
for each month.

so for each month depending on the amount of staffs holidays pending onl 10%
could be if i went over the 10% the the cell would go red to tell me that
there are no more holidays available for that month.

would be greatfull if anyone could help.