Comparing Values in Dissimilar Spreadsheets to find and identify matches

BCWITHE 

Would it be OK to highlight entries that do not have a match? If so:

Select column B. I'll assume that B1 is the active cell in the selection.

On the Home tab of the ribbon, click Conditional Formatting > New Rule...
Select 'Use a formula to determine which cells to format'.
Enter the formula

=ISERROR(MATCH(B1, Sheet2!C:C, 0))

Click Format...
Activate the Fill tab.
Select a highlight color.
Click OK, then click OK again.

You can also try

=COUNTIF(Sheet2!C:C, B1)=0

as formula