New Post: Black and white pixels while legend is only colors

I have some black and white pixels in my image while the legend has only shades of green for values >0 and grey for values =0. It seems that the grid value of these black and white pixels is always 0.

I noticed that when I have a green patch, pixels west of my patch tend to be black and pixels east tend to be white which makes me think that this is some kind of shade effect.

Any ideas?

thanks