Version: 1.8.9-4.0.0.39
When looking certain entities whilst a slimeling is in view, they appear to change color based on the color of the slimeling:

Doesn't seem to affect armor:


(Note that sometimes entities further away will be colored, sometimes both, and sometimes only closer ones:)


It's a virus!

Can't reproduce in development. I think its fixed.
Thank you for reporting.
I fixed this in https://github.com/micdoodle8/Galacticraft/commit/671751e00745afd3586633f6598097fb4ddd6ae3
So this shouldn't be a problem in the latest 1.8.9 beta build.
Most helpful comment
It's a virus!