Dyeing Gray Hair with Cassia: Mix Rhubarb Root Powder before or after Cassia dye release?

In this video I test the difference in colour and dye uptake between adding Rhubarb Root Powder to the Cassia mix before and after Cassia has dye released. My conclusion is that there is no difference in colour and dye uptake between the 2 options but in my opinion both options look worst than when rhubarb root powder is not added to the mix at all (I got unnatural yellow greenish tones), See below the products I used:

Khadi Cassia Obovata (http://amzn.to/2xIDqSh)
Rhubarb Root Powder (http://amzn.to/2xH1GnM)

Видео Dyeing Gray Hair with Cassia: Mix Rhubarb Root Powder before or after Cassia dye release? канала Curly in Germany