Hunting sword - weird color

[Drabant1701]

I recently bought a indian hunting sword. I know it not actually made for hunting, and is more of a novelty item, although it is sharpened. But I liked it, so I bought it. I noticed that the upper half was lighter, and the side toward the edge was darker, both left and right side are the same way.

I wanted to lightly etch the sword with lemon since I saw watered steel. So I cleaned it with oil and 0000 steel wool. Then degreased with soap and after that alcohol. After that I etched it with a lemon for 10min, dryed and oiled it. I was pleased with the etch but the sword i still darker on the bottom half. It is hard to show in a photo and is more obvious in real life.

The question is: have anyone seen this on other swords? What could be the cause of this difference in color?

My thought was that someone has sand papered the upper half, and that is why it is lighter and wont etch as much. Or thay the edge has been hardened with heat and therefor is darker. One thing that is a little odd is that there is a streak of dark in the light section and its on both the left and right side, in the same place. Now this had me thinking that it may actually be the steel itself that is darker on the edge side, on purpuse or not. Im rambling a bit it may well just be dirty, I cleaned it well but I wont use anything more than 0000 steel wool and wont etch again so it is all just speculation.

Any opinions are welcome.