Why do I have black discolouration on the tip of my penis?

I am a 32 years old man and have noticed a bit of blackness near the tip of penis (glans penis) for the last few days. Is this normal to have blackness near the tip? I am unmarried and have not had sex but I do some masturbation. Few days back I had minor pain in my glans and chemist prescribed me an ointment Fucibet from Ranbaxy (antibacterial corticosteroid). I applied it for two days on my glans and then stopped it as the pain relived. Please advise.