LOL! Yup. The first two external tanks for the shuttle program were painted with white latex paint. From #3 onward, no paint due to weight savings initiatives.
A tale of Yore: Early in FedEx’s history, they had a bonus program for cost savings accrued through employee suggestions. At the time, all FedEx aircraft were all painted in blue and orange.
One night at the Memphis hub, a mule driver got the bright idea of eliminating the paint job to save weight in favor of a FedEx logo only on the tail, and submitted the suggestion.
The idea was accepted, as it allowed each flight to carry substantially more cargo weight. I was told the employee’s bonus check was in the millions of $$ range, as it damn well ought to have!!