Thanks! Washing it with Dawn dish soap and warm (hot?) water in the sink should remove the oil. Let it soak and you may have to wash it more than once. Stuff with towels to shape it while it dries for the first day or two.
Can you post pictures of your bag? I have never used neatsfoot oil but sometimes conditioning with Black Rocks helps to even out coloration.
Below is a link for a dark brown PL that I rehabbed. It had a nasty spot and it was ripped so I took it to the cobbler to professionally repair the damage before I rehabbed it and it came out great.
http://forum.purseblog.com/coach/a-tale-of-2-patricias-double-rehab-reveal-765238.html#post22491820
Another option is to buy a small jar of leather refinish restorer dye and try and cover the spot yourself, see link below, but please post pics here for advice first. Good luck!
http://www.wood-n-stuff.com/leatheraid.html