An aqueous or alcoholic solution of gentian violet or methyl violet is one of the best.
This has been well shown by Churchman in his work on gentian violet.
The best stain for acetic acid preparations is, perhaps, gentian violet.
gentian violet gen·tian violet (jěn'shən)
Any of several basic dyes that are derivatives of pararosaniline, especially a dark green or greenish mixture that is used as a biological stain and as a bactericide, a fungicide, and an anthelmintic.