解説Lake pigment made from aluminon and ferric ions.jpg
English: When aluminon binds ferric ions (Fe3+), it forms a violet colored lake pigment (an aluminon complex salt).
Pigment in the picture is in neutral solution, and was made by combining aqueous aluminon and FeCl3.
Source for claims:
Clark, RA; Krueger, GL (1985). "Aluminon: its limited application as a reagent for the detection of aluminum species". The Journal of Histochemistry and Cytochemistry. 33 (7): 729–732. doi:10.1177/33.7.3891845.