No doubt there will not be universal agreement with my opinion, but I do not think the toning is original. It looks similar to coins that have been exposed to a dip and high sulfur content to produce the color. This would greatly affect the price in a negative manner.
It's very difficult for me to place a value on the coin because I try to avoid buying and selling what I consider problem coins and this piece looks to fall within that category. The best I can say is that the market for it might be limited somewhat and that you will get a wide range of values thrown out there. Since you purchased the coin relatively recently, a good guide for you might be what you paid for the coin.
I agree with Tom (as usual, he knows what he is talking about) it looks artificially toned. It's a shame too, it looks like it would have been a nice AU-55. I do suspect that someone was covering an old polish job, the reverse shows some really glossy details. Spend it...
It does look like the photos were taken using a single light source from a low angle which would certainly emphasize the toning. It is so hard to evaluate any coin by photos but more so for toned ones. As it is presented, it does look like it might have been treated. Machete, what does the edge of the coin look like as far as toning?