If your Brooks saddle is brown or honey color, then using other stuff like mink oil etc on it will make it darker. My husband used either linseed or neatsfoot (I forget which) oil on his honey Brooks and it turned a dark brown permanently. Nice brown, but no longer honey colored.
I have used only Proofide (and lots of it) on my 2 honey colored Brooks', and they did not change color at all.
Riding on your saddle before PH'ing it will not hurt it, unless as Mimi said, you get it wet. Never a good idea to ride a wet Brooks- it can wreck and warp the shape!