completely confident that you can do it. From what you've said you have some experience dyeing, but have not been satisfied with the turn outs. That tells me that something needs to be tweaked in your method, but you already know the basics.
It may be that you want to go pick up a $2 skein of wool and practice on that rather than risking your good yarn. That's perfectly understandable. That's how I started - with Patton's wool that I found on sale. Now I sell my dyed yarn at the LYS. And I only work with food grade dyes - I haven't touched acid dyes in years.
To get a true indigo, you're going to need a LOT of blue and just a touch of red. TBH, I find it easiest to keep things simple. Working with icing colors, I'll dissolve a chunk in a small jar of water, then use an eye dropper to transfer some of it to the dye pot. Then if the dye bath exhausts before it's done (maybe it's splotchy or maybe it's too light), I have the dye color already mixed up and I just add more dye to the bath. With things like yellow (which is a tough color to dye with food coloring), I've had to do this maybe 4 or 5 times to get the color I wanted. If you check out my blog
, compare the yellow in the first picture (which doesn't look like yellow, it looks like off-white) with the yellow in the last picture and you can see what I mean (first picture was my first dye job ever). It doesn't hurt anything though, so long as you avoid shocking or over-agitating your wool. Each successive dye bath will get it a bit darker.
Now, if you get the tone of blue you want, and it's not indigo enough, then an overdye with just a touch of red will lead you towards indigo. And again, if it's not enough the first time, do it again. I much prefer overdying lightly, because you can't undo it if you take it too far, but if it's not far enough, it's easy enough to keep trying.