The vast majority of scientific images, be it in papers on press releases, are using an arbitrarily-chosen colormap to map whatever numeric values are there to

The vast majority of scientific images, be it in papers on press releases, are using an arbitrarily-chosen colormap to map whatever numeric values are there to actual visible pixels. For the Event Horizon Telescope speficially – it is a radio telescope, so what it sees has no intrinsic "color" as perceived by a human eye at all. Same with this simulation here.