Changing Leather Color

[whomewhat]

I know I read in another thread somewhere, a shoe thread, about how to change the color of ones shoes using various colors of creams, etc. My problem is similar. I bought an antique 18K Cartier watch for my 9-year old daughter. I also bought an 18K Cartier buckle to go with it. Finally, I purchased a Cartier watch strap, but alas, the color is a very dark blue (Cartier would have to special order the strap I want so I am looking for a less costly alternative). I would like to change the color to as close to a cognac colored brown as is possible. I am hoping that the same process that many of you use to change your shoe colors, antique them, etc., would work for this, especially since I seem to recall that blue creams are added to brown colored shoes to darken it? Can someone please explain to me howone would go about this? Thank you.