Maybe this will work for you. Go to the worksheet you want to shade the
cells on, click Edit/Find on Excel's menu bar, put just the exclamation
symbol in the "Find what" field. If the Options button is showing two
greater than signs (>>), then click the button to open the options part of
the dialog... make sure "Sheet: is selected in the "Within" drop down,
"Formulas" is selected in the "Look in" drop down and that there is *NO*
check mark in the "Match entire cell contents" check box. Once the above is
all set, click the "Find All" button, then press Ctrl+A (this will select
all the cells shown in the table that appeared on the bottom of the panel),
click the "Close" button and, after the dialog box closes, all cells on the
worksheet with a reference to another worksheet should all be selected...
then just fill them by whatever means you currently do (that is, click the
Fill icon in the tool bar if it is displayed or use the Patterns tab on the
Format Cells dialog box).