Is dyeing hair bluish-black forbidden?

Scholars differed concerning the ruling on dyeing hair with pure black, oscillating between prohibition and reprehensibility (karahah). As for what is not pure black, such that it is mixed with another color like red, there is no harm in it, due to the Prophet's (peace be upon him) saying: "The best things with which to change gray hair are henna and katam." Abu Bakr dyed his hair with henna and katam.