Cambridge University Library holds about twenty early modern books whose pages have been painted, stained or dyed a lurid yellow. The reasons why are unclear, but all are religious or legal texts that were printed in London or Antwerp in the mid-sixteenth century to circulate in Tudor England. In many cases, the yellow extends so deep into the openings that it must have been applied before binding; that this is the case for books in contemporary bindings suggests that the yellow was applied for sixteenth-century owners. Although this colour was not printed, it can be considered an integral part of at least some copies of some books, which in turn indicates the need for further research into the role of colour in the Tudor book and print markets.