Throughout baseball history green has always been associated with ballparks. The terms "green diamonds" and "green cathedrals" don't just refer to the field. By far, green is the most used color for seats in the 30 current MLB ballparks.
The dominant seat color in MLB is green. In 16 of the 30 current MLB parks, green is the main color for seats.
Ballparks primarily with green seats: Citi Field, Safeco Field, Progressive Field, Comerica Park, Camden Yards, Angel Stadium, U.S. Cellular Field, Wrigley Field, Miller Park, Chase Field, AT&T Park, Target Field, Coors Field, Minute Maid Park, Rangers Ballpark, Target Field, and the Oakland Coliseum.
Note: Coors Field has a row of seats in the upper deck that are purple. The new Target Field's club level contains some seats that are natural wood.
Most of the rest of the ballparks have blue seats. Nine parks have seats that are primarily blue.
Ballparks with blue seats: PNC Park, Yankee Stadium, Kauffman Stadium, Citizens Bank Park, Tropicana Field, Rogers Centre, Nationals Park, Petco Park and Turner Field
Two ballparks have mainly red seats. Great American Ballpark and Busch Stadium. This makes sense as the teams that play there are the Reds and Cardinals...
Note: Busch Stadium has some green seats in its club areas.
Two teams fit into the "mix" category:
Dodger Stadium: Pictured above, Dodger Stadium has a different seat color for each level. The field level has yellow seats while the Loge level has orange, Reserve has a pastel green color, and the Top Deck has blue seats.
Fenway Park: Fenway has three different seat colors. The grandstand has dark blue wooden seats, the field boxes and loge seats are red, and the bleachers are green.
The Florida Marlins play at what is now called Sun Life Stadium. The vast majority of the seats are orange. Some club level seats are a teal color.