Comments inside protocol conformance aren't colored

[ZevEisenberg]

You should be able to see the issue in GitHub's syntax highlighting as well:

@interface ABCSpreadsheetView () // correctly highlights as a comment
< // should highlight as a comment
ABCRowHeaderViewDelegate, // should highlight as a comment
ABCSpreadsheetLayoutDelegate,
UICollectionViewDataSource,
UICollectionViewDelegate>

Admittedly, this is a slightly unorthodox way of wrapping protocol conformance, but it minimizes source control churn on lines that are not really changed when a conformance is added or removed.