I've only coloured soap with alkenet once, bout a year ago. I got nice dark purpley color. I added about 1 tsp ppo. I know some people prefer infusing their oils but this was a last minute addition
Hope that helps!
I infuse olive oil with powdered alkanet. Then use about 25g of oil to colour about 750ml soap batter. Gives a nice dark purple. It will fade a bit over time. Keep the soaps dark in storage.
Wonder if gelling is a big factor when using alkanet powder infused oil. I have never had it come out purple or even close, but I very seldom let my soap gel