I am a traditional Indian girl who used to henna tatto my hands all the time. so here goes my experience.
Henna turns black when kept unused,its natural and doesnt mean it has gone bad. As far as you dont see fungus forming on top of that it is in good shape.
if you mix it really well, it should come back with a dark green color again.you can add warm water to it to bring it back to life. Also another quick test you can do is to apply just a tint little bit of henna on the under area of your foot and you can see the orange color once you remove it in couple minutes.Hope this helps
3a with some 2a-2c, Medium/Low Porosity
Co-wash:deva no-poo/Vo5 kiwi
Leave-in:Shea Moisture/GVP conditioning Balm/AOHSR
Since long hair- I finger twist in big chunks, which helps till 5th day hair
Plop: Old T-shirt for 15 minutes ,diffuse