My original question was Conditional format based on non-blank previous cell but i now realize that it was the wrong way to go. I don't need to format based on what the prior value was, just if the cell is blank copy the format from the previous cell.
I need to conditionally format a blank cell based on the previous cell
A B C D E F G
AC BW IN
BW BC ST IN
B1 has a conditional format based on the value AC. C1 is blank so it should get the B1 format. D1 is blank and should get the C1 format. E1 is nonblank so it gets whatever the conditional format is.
The values in that will turn the formatting on come from a list of values i.e. AC, BC, IC, SC.
What i don't understand is how to copy, in the formula itself, the value of the previous format.