making my error message show a blank cell when printed

I am using two drop down boxes to determine a end value that is the weight for a work out. the first box is the category (upperbody, lowerbody, etc) that the determines which list is set in another cell in a drop down box. so if lower body is set in the first box, only my list of lower body movements show up. This works great thanks to some help I got recently on the forum.

The problem I am facing is that I expect some lifts like squat to plug into a formula and return a weight based on a percentage calculation. When I choose a lift that is not based on a percentage calc. It shows an error (rightfully so).

What I need is that cell to show up blank so my students can write the weight in that they used on those types of lifts.

What I tried: I tried conditional formatting so that formula =ISERROR(reference) turns text white. The problem is the text stays white even when I change the drop down box to a value that returns a number.

since within the formula there is always a chance for an error to be returned is there a way to set the format for only what is showing up and not every possible outcome.

Thank you for the reading and thank you for the help!

still having trouble. Here is the calculation.
=INDIRECT(A8)*C10

How would it look using the error checker
=IFERROR(calculation, "")

If there is an error will this just leave it blank? thanks a ton!!!

That worked perfectly thank you for following up!!!