if it only would be Haythornthwaite, I would say this is one of his typically mistakes. But as Albrecht Adam mentiones this too, it must have a reason. Maybe the green coloured out or it was one of Murat fancing colours like "Azul-blue" or something else which you can see as green and blue.
So with this source I think your figure is ok and researched Beside this the excellent paintjob of course!
I haven't taken your comment as racistic, it is just the ordinary point of few about the Neapolitan troops in the Napoleonic wars. But I don't think, that it is really right as memoires from Italian officers showing another picture of them. For example in Spain General Pepe wrote that his regiment was of a very good moral and high qualitiy after he reorganised them.