Yes, David, from eye witness stories, No. 4 did get that bad too.
And indeed, that's how very badly worn once-maroon paint can get, when left outdoors for years and painted on wood. It is possible - indeed, probable - that it was the cheapest quality paint they could get in the first place!
There are photos available of a Cavan & Leitrim coach still in service in GSR maroon well into the 1950s. The maroon on it is just as bad! A nondescript browny reddish colour. GSR maroon was initially like BR 1960s coach maroon, or LMS maroon - the same shade. Again, there's the proof of how scrappy it can look.
Contemporary British fans will testify to how scruffy even a (steel sided!) BR Mk. 1 could look in worn maroon. I saw this myself in north Wales in 1970.
I suppose the key is to have an uneven finish on your models, so it doesn't look as if the worn shade is the way it was initially painted; also maybe to make one look a bit tidier than the other, to emphasise the unkempt appearance of what you choose to be the worse of the two!
Incidentally, remiss of me to omit to initially mention the sheer class of these models. Fantastic work, fantastically interesting prototypes. Arigna Road just keeps getting better!