Cit,
I don't have the JG300 book that just came out, but I think that further research will show anyone interested that JG300 was somewhat unique in their color schemes. Any interesting photos, or decals, or profiles that I see are usually JG300 or JG301.
There are several exceptions to this rule, including a really werid looking pokka dot G model and variations on this which did not belong to this unit.
I have seen photos of pilots painting their cowlings to suit them, maybe this was such a paint job.
Also don't forget that while the RLM colors were the same, the factories did do custom paint for the Units at one point. Whether this continued up to the end of the war I am not qualified to comment on.
The LW color schemes were locked down. In fact I be more suspect of one that looked exactly like the other.