The paler seasonal beer style that became common at Oktoberfest in the late 20th century was Festbier.
For much of Oktoberfest’s history, the festival’s traditional beer was Märzen, an amber-to-copper lager associated with brewing in March and storing beer through the warmer months. It was maltier, stronger and darker than the beer most visitors now expect at Munich’s festival.
From the late 20th century, Munich breweries increasingly served a lighter, golden lager known as Festbier. Its paler color, lighter body and comparatively easy-drinking profile suited a festival where visitors might drink several large measures over a long afternoon. The change is often dated to around 1990, when the golden style became the standard at the modern Oktoberfest.
A common mix-up is treating Märzen and Festbier as identical. Both are associated with Oktoberfest, and breweries outside Munich often label amber Märzen-style beers simply “Oktoberfest.” At Munich’s official festival, however, the modern standard is pale Festbier, brewed by the authorized Munich breweries.