The Boston Arts Academy has the band Dispatch — and about 200 volunteers — to thank for its new look. The local rock act, which started its Amplifying Education Initiative to get people to volunteer to fix up schools, spent Saturday repainting the academy, which is Boston’s only public school dedicated to the visual and performing arts. Also helping with the cause was City Year Boston and Radio 92.9. Later that night, the band played a gig at Agganis Arena.