Probably the first trichrome method was that of Frank B Mallory, an American pathologist, first published in 1900.
[1] Unfortunately, none of Mallory's publications (they go from 1891[2] to 1938[3]) provide any explanation of the rationales of either his trichrome or his phosphotungstic acid-haematoxylin (PTAH) method.
Mallory's trichrome method, using acid fuchsine followed by a solution containing PTA, orange G and aniline blue, provides dark red nuclei, orange erythrocytes, and blue collagen fibres, cartilage matrix and mucus.
[4] In 1915, M. Heidenhain introduced azocarmine G in place of the acid fuchsine of Mallory's method.
Heidenhain also introduced visually controlled destaining to provide for different colours in cell nuclei (dark red), collagen (blue) and a variety of colours in cytoplasm.