Excel vba double checker

I have looked for this around but i didnt see any code that did what i needed. I want to create a vba to check between 2 excels(preferably by opening an open window), excel 1 and excel 2, the first one should first check into the second using 2 values from 2 columns (date and price), and any one that doesnt find a match should be marked with red, then excel 2 should excel 1 in the same way back, highlighting in the same color for simplicity sake.