Jack,
If you want conditional formatting, this will work ...
Select your Numbers increased by Stars sheet, select the column with your numbers in it, and name the range 'Numbers' (Insert -> Name Define). Do the same for your Compare sheet, but name that range 'Compare'.
In your Numbers increased by Stars sheet, select column A (or your item number col), select conditional formatting and type this in the Formula Is ...
=(A1<>"")*(ISNUMBER(MATCH(A1,Compare,0)))
Now go to your Compare sheet and select the entire column of item numbers there. Again choose conditional formatting, Formula Is ...
=(E1<>"")*(ISNUMBER(MATCH(E1,Numbers,0)))