Mixing colors at the intersection of tiles in Slick2D

I’m just learning Slick2D.
Can you please help and tell me how to properly mix colors on adjoining tiles? I would like to get the same effect as on the right in the picture.

Right now, I’m just using the Image.draw(x, y, Color) method. The color is applied, but it is different between tiles. (the sprite in the example is the same)

enter image description here