Is this a new saddle, or a used one that is still light colored? I get new leather tack, use Leather Honey on it, and it does darken several degrees just with just that. Also leaves the leather a LOT more flexible and soft. I am still working Leather Honey into my new western saddle, needs a couple coatings to get it softer, able to turn the stirrups. The light areas are coming along nicely in “browning up” so saddle isn’t quite so glaringly light colored. This is going to be a using saddle, so not “looking like a rookie” with a new saddle is part of my goal! I always have liked how well used saddles brown up with being conditioned, sweat on, exposed to the sunshine of use. Lovely shades of brown to me!
http://www.leatherhoney.com/
Leather Honey used to be called Harness Honey, is a great product. It isn’t cheap, but does go a very long way, is excellent for leather. Not for synthetic products or shiny stuff like Patent leather. I am a convert, once I got some and tried it.
You probably should get some scrap leather the color of your saddle, do some experimenting with the dyes before tackling the saddle. You could get the light leather scraps from a saddle repair place. You may need to mix a couple of the shades of brown, to get a color you like. Write EACH recipe, so you can repeat the combination in correct amounts for the color to be consistant on the entire saddle. Then after dying leather, you will need to work in conditioner, so leather dye gets down into the pores of the leather and stays in.
The bottles you show have a fair amount of dye, but for a western saddle, I would think you need at least two that size, to have enough for all the layers of your saddle. Get some extra daubers, like what comes with the dye. They get kind of hard after being used. You may need to do two dye coatings or touch-ups after letting saddle dry for a couple days, so extra daubers will be handy. If you mix the colors, obviously you need more bottles of both dyes, so you can combine them and have enough.
Talk to the saddle repair folks, get some tips or help from experienced people that dye leather regularly. Our local repair folks are really helpful, you could call and ask for help if there is no local places. Ask for Tom or Vicky, they work leather in the repair shop.
https://www.tomswesternstore.com/index.php?route=information/contact