MCL39 on Thursday, but in a camouflaged livery. Why are F1 teams introducing their cars in temporary colour schemes?

When teams perform a car launch, they claim to be launching their new car in full for the year (though some look to deceive their rivals with what is unveiled), and a livery launch simply pulls the covers off the new colour scheme on the next cars, with the updated paintwork placed on either a show car or previous model from the team.