have you seen the rainbow on the meat slices? It can be found in many sliced cured meat products or fresh meat slices, which goes like this:

I also took a picture of the iridescent color on a piece of beef while eating the other day, but this is basically only a little yellowish green:

first of all, this color does not appear because the meat has gone bad or has been contaminated by some strange substance. This color does not come from chemical pigments, but from a "structural color". In this case, if there are no other abnormalities, then the meat can still be eaten.

structural color is the color produced by the special physical structure that affects the propagation of light. For example, soap bubbles show color, which is the result of film interference, not because the liquid on the soap bubble contains colored substances. For example, the sparkling blue on butterfly wings also comes from a special microstructure:

(more reading: dynamic picture appreciation: butterfly color, of course, butterfly body actually has some other pigment colors)

but there are generally two explanations for the production of iridescent on meat slices: the cut and neatly arranged muscle fibers on the surface of ① meat slices form a "two-dimensional diffraction grating", which produces color. The multilayer structure in ② muscle tissue causes light to be reflected and refracted many times. In this process, the interference of different reflected light will strengthen or weaken the visible light in a specific band, thus changing the color.

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the right and left sides of the following image correspond to these two explanations respectively:

some people have specially studied the microstructure of these "iridescent flesh" under the microscope, and it is found that the structure similar to the grating and the multilayer structure that can form interference are available, but this iridescent performance is more like the interference caused by the multi-layer film structure. (for more reading, see "read the original text")

below is what "iridescent ham" looks like under a microscope:

(the picture is a scanning electron microscope photo, and the electron microscope photo itself has no color. However, the real color observed in the corresponding position under the optical microscope is superimposed at the later stage.)