Yes, greyscale is available under the accessibility options, as well as red-green and blue-yellow variants. There is a shortcut option as well, which enables a small slide-out overlay button on the lower right edge of the screen. There may be an app that allows you to configure this toggle via another gesture or icon.
@aspentremble I just noticed there is a quick tile for color correction as well, so you could simply pull down your notifications and toggle it as needed.