This is relevant to the current beta at time of writing. I’m using version 1.3.14-beta1. If an Image is created in the gray ColorMode, then its GraphicsContext is used to draw some antialiased shapes, there is a dark halo around the shapes’ edges.
This does not seem to be a problem with RGB color mode.
As a workaround, I wrote a Lua script method to loop through the image pixels and divide the gray value by the alpha. However, the fast version which sticks to integer math results in variation in the values.
Above, 0x8b varies with 0x8c.