I'm having good luck with the Lexol conditioner. I'm using the Spirit Dye in all colors too...Oxblood Red, Navy Blue, Purple and Grey. I'm using the following process:
1. Deglazer
2. Dye
3. Burnish to rub off excess dye and shine, let sit overnight
4. Lexol Conditioner with a soft cloth, let sit overnight, to get soft again
5. Acrylic Resolene Finish
The Lexol does not seem to darken the leather with this process. Also, if you use the deglazer, and put the dye on when the leather is still damp with deglazer, you will need to use less dye and you will have a lighter result. Another solution is to use a product to reduce the dye, to get a very light brown so that when you use Neatsfoot, you get the right shade. I'd practice on scrap pieces until you get the shade you want. The above process works great for me though.