Curiosa: Scribbleamus igitur, iuvenes dum sumus!

Coloring in the odd figure in the illustrations of your 1533 Venetian edition of Virgil's collected works (accuratissime castigata, et in pristinam formam restituta, cum acerrime iudicii virorum commentariis) -- well, hey, the princeps poetarum (not to mention his commentators) can get a bit long-winded when he's hip-deep in an epic simile, and doodling keeps the hand busy while the mind grapples with the text.

Coloring so thoroughly that ink bleeds through the paper and obscures the text of not one but several neighboring leaves might, however, be construed as absence of mind, if not outright vandalism.

Drawing a mustache and beard on Dido merely demonstrates your childishness.

Thank goodness you got bored like everyone else and started skimming after book VI of the Aeneid. Or so I judge from a sudden absence of ink blots.