I need to highlight (e.g. by font or background colour) rows which
contain a value that is NOT present in a reference range.

Column S of the reference range contains an account ID code.

In the range being compared, I want to highlight new accounts which do
not exist in the reference range. The new range has a different
layout to the reference range because its a CSV file of payment data
downloaded from an assortment of third party web sites, but lets just
assume for the current example the ID code is in column C.

I know there are a variety of methods I could use including
highlighting all and then looping through the IDs in the reference
range, unhighlighting all rows where the ID appears in the new range.

But is that the fastest way?

What is the most efficient way to code for "if this ID code doesn't
appear in the reference list, highlight the row in bright blue"?

Travis