Part of an image is grayscale, while the other part is not

[#1]

For some reason, this image of this Ducks Bill, is grayed while the other parts are still colourful.

[#2]

For some reason, this image of this Ducks Bill, is grayed while the other parts are still colourful.

[#3]

Look under the View menu. Do you have the Gamut Warning turned on? If so, you may have accidentally turned on this feature via the menu or its keyboard shortcut. This option is a toggle so selecting it a second time deactivates the feature.