Conditional formatting for a cell that has a formula in it?

So I'm working on a budget, and in a cell I have and =IMSUB formula. I'm trying to format that cell so that it turns green for a positive value and red for a negative value, but no matter what I try the cell stays green regardless of the number. Can someone help me?

If Positive value is shown by having "+" in the result (as IMSUB returns a TEXT field) then

=ISNUMBER(SEARCH("+",B1)) Green

in CF will give the required results

=ISNUMBER(SEARCH("-",B1)) Red