The EM picture image exists so do images using other non-optical techniques such as ATM - atomic force microscopy, MFM - magnetic force microscopy, UVM - ultraviolet microscopy, IRM - infrared microscopy, PAM - photoacoustic microscopy, even high frequency radar or sonar images. All usually collected in gray scale. There’s usually a handy-dandy option on the instruments to colorize it for analytical purposes. Some people prefer to do their image analysis in gray scale. They say its better (usually old farts like me!) others prefer colorized. It used to be you couldn’t get the dynamic pixel range in color as you could in grey scale. I don’t think that’s true now. There’s colorization services you can have done on old pictures! You going to tell me those people don’t exist?