Ah yes, that is the result of a virus. If you have other tulip bulbs (or lilies) in the vicinity, you ought to remove it now as it will spread to other susceptible bulbs. Whilst the striped effect can look pretty (and was, in fact, the reason for all those striped Rembrandt tulips made famous in the Dutch tulip bubble), the virus will weaken the plants which will diminish over the next couple of years. Of course, many people grow tulips as annuals anyway, in which case, enjoy the variation and dispose of the bulbs when blooming is over.

Thank you, Camp.... good to know! They've blown now so I'll dig them out.