Mae, do a search for glycerin soap dye. There are several companies that sell pre-mixed colors, dispersed in glycerin. Unfortunately I've not ordered from any of them, so can't vouch for them.
Here's one that looks promising
http://www.cierracandles.com/liquid-gly ... d-dye.htmlbut many other vendors carry similar products. To this purple, I'd add a touch of black liquid colorant from the end of a toothpick to get a deep purple.
I have a great navy blue liquid colorant and I just added a spec of liquid red and got a great deep purple. Unfortunately, company is no longer in business.
You might call Bramble Berry and ask their advice. They have this one
http://www.brambleberry.com/Liquid-Blue-P4055.aspx Question for them is what happens if you add red to it and in what ratio to get deep purple? Some get grayish/muddy looking.
They are very good on stuff like this.
Connie