you could try this:
I have these two columns (column "A" and column "B"). I want to color them when the values between cells in the same row mismatch.
Follow these steps:
Select the elements in column "A" (excluding A1);
Click on "Conditional formatting -> New Rule -> Use a formula to determine which cells to format";
Insert the following formula: =IF(A2<>B2;1;0);
Select the format options and click "OK";
Select the elements in column "B" (excluding B1) and repeat the steps from 2 to 4.