Topic: Unwanted purple hues

Hi nomicons/smile

So, I've been experimenting with different ratios of MM henna and indigo. I keep my recipe very simple: henna, indigo and boiling (filtered) water. For a while that was it. But the indigo would wash out super fast leaving my hair a very dark reddish brown (super nice!) and my greys a bright red (not so nice).  So I decided to try adding a little salt to the indigo mix, applying the henna to dry hair and it worked! Fading was reduced and no annoying orangy greys. I notice my hair is taking on a purple tinge! A very dark burgundy. And this is on my normal hair, not my greys. Greys stay reddish. I used a 1:1 ratio of henna and indigo a couple of times till I noticed this. So I went back to a 2:1 ratio of henna and indigo but looks like the purple hue is being resistant.

Any suggestions to neutralize the purple and bring out the red-brown? Ah, and I've been leaving the henna in for 2-2.5 hours. Maybe if I leave it longer? Let the henna deposit more?