sixpenceee:

A diaphonized creature is a transparent creature whose skeletal structure is visible. Their cartilage & bones are highlighted by rich reds, purples, and blues.

It was first developed in 1977 by the scientists G. Dingerkus and L.D. Uhler. First the animals are rendered transparent by bathing in a soup of trypsin, a digestive enzyme that slowly breaks down their flesh. They are then soaked in several batches of bone, muscle, or cartilage dyes, to get the appropriate stains. (Source)