I just got a brand new pair of Iron Ranger's in Amber Harness color and have been doing a lot of research regarding leather conditioner/boot oil that won't darken the leather.
Sounds like the mustang paste works well, but I also been reading that the Bick 4 by Bickmore also will not darken the leather. I think I'm going to give it a try since it is much more available and accessible than the mustang paste. I'll update everyone if I end up going with the Bick 4.
Also, I contacted Red Wing directly and inquired about their different products. One rep indicated that the All Natural Leather Conditioner and the All Natural Boot Oil both contain the same ingredients, but the conditioner would darken a little less than the oil would.
I still think I'm going to go the Bick 4 route though as everything I've read indicates no darkening of the leather when used. Again, I'll post back with before/after pictures.
If anyone has only utilized Red Wing All Natural Leather Conditioner or their All Natural Boot Oil on Amber Harness leather, please comment on how much it has darkened the leather since new.