Conditional Formatting and Errors

Hello all,

I made a calendar that collects data from another tabsheet by looking at the month and daynumber. When there is no occurrence it displays a #N/A.

I thought about using =IF(ISERROR(OriginalFormula),"",OriginalFormula) to hide the errors but the formula is too cumbersome for that.

Another possibility would be using conditional formatting =ISNA(A1), but, not all cells have the same color, which makes it quite difficult to apply.

Another conditional formatting is in use for displaying weekends by looking at the year.

The attachment will show what I mean

Any ideas?