I would use conditional formatting for this. Have you ever used that?

If you give the master list of Stocks ticker symbols a "named range", something like OurStocks, then you could use that name in a conditional formatting formula.

Then on the portfolio listing, highlight those tickers and apply a CF. Let's presume you highlighted cells A2:A100, ok? After highlighting those cells:

1) Click Format > Conditional Formatting
2) Click Condition1: Formula Is
3) Enter this formula: =COUNTIF(OurStocks,A2)>0
4) Click Format...Pattern...Yellow color (or your choice)
5) OK

Now all the ones that are in the OurStocks named range will light up for you.