Yes it's true.
Moldy meat can have gangrene
and be colored black white
gray or blackish green.
That is why those who sell
the pieces of murdered cows
.. the subdivided cadavers
want red food dye
sodium nitrates and nitrites
to hide the danger and make
it invisible in the light.
*
Footnote: moldy meat often
has more moisture than average
and a grainy texture.