Related Clues:

• Henna, for one
• Litmus, essentially
• Stuff in a robber-foiling pack
• Rich treat
• It may be red
• It changes locks
• Salon application
• Food additive
• Salon goo
• Textile company purchase
• Indigo, for one
• Turn red, perhaps
• Just for Men, e.g.
• Salon goop
• Spot remover?