Your dye isn't going to come out nearly as dark as the undiluted dye looks anyway, so I wouldn't worry about the blue. The red may come out pink. In my experience there's no real way to get it darker, the plastic's gonna absorb as much as it can and that's that.
Also, know that the dye isn't going to take uniformly. If you do it right it'll be good coverage and still look nice, but you need to know that it'll never be uniform. You'll have lighter and darker areas all blended together... kinda like anything real that's been slightly weathered.
My advice? Don't have your water too hot. bring it to a boil and then turn it down a bit until it's just bubbling around the edges.
Don't leave your parts in longer expecting them to take more dye. They won't and you'll warp your parts. That is why my C. Wing Saber doesn't transform correctly anymore. A few seconds... let's say 10... ought to be enough, then you need to dip the part in ice water immediately and hope you don't warp anything.
I guess just practice with a junker bot and see how it works out for you.
Good luck!!
*edit* P.S. I would avoid acetone in the water at ALL COSTS. It's not REALLY going to help much and it can ruin the whole show.