The team, the last factory outfit to reveal its new livery, made the unveiling on the eve of the final pre-season test at Jerez.
It has used interim liveries for reigning champion Lorenzo and seven-time title winner Rossi thus far in testing.
Rossi's return to the team is reflected in increased Monster branding on the side of both bikes.
Yamaha MotoGP launch gallery
With no title sponsor however - a hangover from Fiat's 2010 exit - the team has kept its corporate blue and white colour scheme, with Rossi's #46 in yellow and Lorenzo's #99 in red.
Although Lorenzo captured the 2012 riders' title, Yamaha was outmatched by Honda in both the constructors' and teams' races.
Yamaha last won the two titles in 2010, in what was Rossi's final year with the squad before his switch to Ducati.
The final MotoGP test at Jerez runs from March 23-25. The season-opening Qatar Grand Prix follows a fortnight later, on April 7.