General Motors' Chevrolet dealers in Michigan like to show off vehicles on social media by placing them in front of recognizable landmarks.

But when they recently put a photo on Instagram of a Silverado pickup in front of the Fort Gratiot Lighthouse — one of the most famous lighthouses in the state, maybe even the nation — a group of eagle-eyed history buffs took to Facebook to point out a gaffe, which has since been fixed.

In a March 7 post on the Port Huron Museums Facebook page, it asked: "Chevy got one thing very wrong about the Fort Gratiot Light in their recent ad at the lighthouse. Do you know what it is and why it's that way?"

The post contained the photo of the Silverado parked in front of the lighthouse, a CGI-installed yellow beacon beaming from the top of the lighthouse. There were humorous replies such as from a woman named Keri Ann, "The fact that a Dodge Ram would look better parked there is the only thing I can think of."

But most of the comments nailed it: The CGI-added yellow beacon was the wrong color.

"Fort Gratiot Lighthouse has a GREEN light. It was changed to green in 1934. This green light was installed so ships could tell the difference between the lighthouse light and train headlights of the engines that were going to the paper mill and other industries along the riverfront," wrote Shannon Kay in the comments.

She and the others who said the light should be green, are right, according to www.fortgratiotlight.org. It reads, "An electric oscillator fog signal replaced the steam whistle in 1934, the same year the tower’s light was changed to green."

The 82-foot-tall lighthouse sits at the entrance of the St. Clair River from Lake Huron. It's Michigan's oldest lighthouse, according to www.porthuronmuseum.org. It was first built in 1825 where the first Blue Water Bridge stands. But that was a bad location and the poorly constructed lighthouse crumbled into the river during a bad storm in 1828. So in 1829, a new lighthouse was built at its current location where a Coast Guard station and the lighthouse watch over one of the busiest waterways in the world.

Its green beacon has a 14-mile range and shoots a half second flash every six seconds, according to an article in www.bluewaterhealthyliving.com. "The green lens also doubles as the cap for its festive wardrobe during the Christmas Season," the article states.

Chevrolet spokesman Sean Szymkowski, who said Friday the dealer team that produced the photo is now aware of the mistake and will update it with the correct beacon color, confirmed Wednesday it has been corrected.

"It was a social media post that the local dealership association created in Detroit," Szymkowski said.

Spokeswoman Erin Robinson of Strive Creative, the ad agency of Metro Detroit Chevy Dealers Association, told the Free Press on Wednesday that it is "all about supporting and highlighting our wonderful local communities, and the reasons we are proud to call this home. While we made an unfortunate mistake on a key detail with the Fort Gratiot Lighthouse," the group hopes the corrected post will bring awareness to the history of the lighthouse.

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Content in this story was edited after publishing.

Contact Jamie L. LaReau: jlareau@freepress.com. Follow her on Twitter @jlareauan. Read more on General Motors and sign up for our autos newsletter. Become a subscriber

This article originally appeared on Detroit Free Press: Chevrolet dealers' post gets Fort Gratiot lighthouse light wrong