如何在iOS中更改部分透明图像的颜色？

I have a single-color image that has partial transparency. I have both normal and @2X versions of the image. I would like to be able to tint the image a different color, in code. The code below works fine for the normal image, but the @2X ends up with artifacts. The normal image might have a similar issue If so, I can't detect it on account of resolution. I have a single-color image that has partial tr