I know the story about Clusius ( I work at the Clusius lab,!) and Busbeq. I don't doubt het got them in several colours from seed. Does that prove that these were already cultivated tulips? I don't think so as several species can be found in the wild with a mixture of colours Like T clusiana and T kaufmanniana. In the wild there are many too with mixed colours I saw beautifull yellow edged T greigii ( normally red)in the wild. A different colored edge often comes from unicolored parents.That is not due to a virus