My not so elegant solution: I filtered all rows by year 2015. I then copied the list of filtered sites in year 2015 and pasted on another sheet; selected 'remove duplicates'. I then had a manageable list of sites. I went back to my spreadsheet, removed the 2015 year filter. Then I filtered by site, selecting the sites I retrieved by removing duplicates. I then selected visible cells (F5, special) and applied a text color for all visible rows. I then selected sites with automatic color, then filtered with year 2016, got my list of sites, and applied a different text color. By using this approach, I can probably make do.