Please follow the steps below to select all the cells with constants:
Step 1: Click anywhere in the worksheet;
Step 2: Click the "Home" tab from the ribbon;
Step 3: Click "Find & Select" and select "Go To Special" from the drop-down list;
Step 4: Select "Constants" in the new window;
Step 5: Click "OK" at the bottom.
All cells with constants will are now in different color. You can fill cells with a background color if necessary.