What does a butterfly landing on a person mean?

The butterfly is attracted to the clothing worn by the person it landed on.

Butterflies are attracted to color, the more color the more attraction, color means nectar, nectar is food. If you wish to attach a special meaning to the event, that is good too, call it lucky, Lucky that the butterfly picked you to land on out of the millions of people it could have landed on, a little like winning a lottery.