multiple values in an array

I'm having a thick moment!!
Basically, i have two columns of numbers. Column a is unique and column J has multiples of column a (though not all column a values match). I need to match and colour each corresponding value. The attached spreadsheet and macro works but i'm not sure how to increase the array so it looks for each value. Some of the spreadsheets i have to check are in excess of 100K rows. Ouch!