Here's a thread where I used straight root beer kandy over a light colored piece of paulownia. It had been stained prior and had an orangeish look to it that I didn't care much for. Using kandy, you don't have to worry with splotches and such. Just get it sealed up and adjust how dark it is or isn't with the root beer, then clear it.
I do a few stocks but
@Bc'z is the man. I do a few but he's a pro at this stuff. I'm posting a link so you can get a better idea of how the root beer can look over a light piece of wood with no added dye or anything. You mention blue, so this might not be what you're after anyway..but at least you can look at it and see the possibilities of just using root beer over what you have. I think your stock would look great like this, myself.
Here's that thread..
Bought a rifle some time back, a Borden B in a Paulownia wood Roy Hunter BR stock. The stock had several minor dents and dings and I don't care for the light color but it has some decent figuring to it. I've got it smoothed out pretty well, not perfect but good. Next up is something I've not...
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