Grouper color variations can be very tricky. Not only does background color change, but bars and spots may either change color or disappear entirely. Without details such as dorsal spine counts and other differentiating features it's very difficult to tell.
There is an interesting old book (you know, those rectangular heavy paper things) I have written by the famous Charles Haskins Townsend: 'Records of Changes in Color Among Fishes', published by the N.Y. Zoological Society in 1930. It includes only Floridian and Bahamian fishes, but has a lot of data describing groupers. The variations documented by Townsend are astonishing. Some of the chages I've witnessed were virtually instantaneous, almost like an octopus. Other color forms are more stable. Townsend was for many years director of the N.Y. Aquarium. His name is appended to several fish species.