Lighter green shades are interpreted as blue shades.

Yup, that's the expected behavior.

The way Yamipa renders images in your Minecraft world is by using maps and item frames. For better or worse, the available color palette for maps is quite limited (not your typical 24-bit color depth), so Yamipa tries to match image colors as close as possible, leading to situations like this:

One possible workaround could be dithering. If I have the time and energy I'll experiment with it and maybe add it to Yamipa.