It's hard to say what amount to use - often you have to experiment with colorants to see what the color becomes in soap and how much to use to achieve the shade you want. I generally use micas so I really don't know if ultramarines fade. I don't have any soap left in which I used ultramarine colorants except for one batch which I just made this weekend. It's too early to know if it will fade.
I noticed BB has a labcolor called Royal Blue. You might want to look at it. Here's a link to where it was mentioned on SoapQueen's blog. It's shown in the top layer in the right hand soap in a picture. It might be close to the color you want and she does mention the amount to use.
http://www.soapqueen.com/bath-and-body- ... or-tips-2/
If it's a little brighter than you prefer, you can add black labcolor or a little (very little) activated charcoal to tone it down. But again, this would be something you have to experiment with and see how it turns out. Of course, someone may be able to give you info on how to achieve the blue you want.
I'm a little concerned about your recipe. The sunflower percentage is about 34% which is a bit high. Sunflower doesn't help with hardness and it may take longer than 4 weeks to really harden enough. It also has a shorter shelf life and may contribute to DOS. I'm not saying your soap will develop DOS but your recipe does have an Iodine value of 79 which is high. I use sunflower a lot in batches but I usually keep it around 10% although I have occasionally used 15%.
Do you have any other oils you could add to the recipe to help increase the hardness?
