Answer: The problem with using neutral polish is that it often ends up with white residue and flakiness, which looks bad on darker colors.
Also, using reno as the only conditioner may not be the best thing. You're better off using a real conditioner like Bick4 or Lexol for occasional (2x per year) conditioning.
GlenKaren neutral creme might be worth a try. I just received some of his light brown, and it's a lot less opaque than other brands I've tried, so it may work well for you. Just test it on an inconspicuous spot first as the light brown did darken my tan boots due to the amount of conditioners in the creme.
This question was first posed and answered in our Official Shoe Care Thread. Have a question and can't find an answer? Want to contribute your knowledge to the community? Try here: http://www.styleforum.net/t/228153/the-official-shoe-care-thread-tutorials-photos-etc