Hard to tell, Patrick, without making a mess of an expensive model! At the very least, you could absolutely weather it within an inch of its life, but the white lining is going to hard to make into anything remotely believable.
So; UTA LOCOMOTIVE LIVERIES
The UTA lining style was a pale yellow / straw colour and red.
Tender and tank sides, and cab steps, had a thin red line inside a slightly wider straw line. Running plates had the red above the straw.
Connecting rods were red inside only.
Boiler bands and outside cylinders had the thin red stripe, flanked on both sides by the wider straw band.
On the BCDR section, numberplates were usually red with raised yellow-painted numerals. I have seen a pic of one (208) which appears to have ploished numerals but it could be the picture. UTA locos of GNR parentage had straw painted numerals on cabsides edged in red.
The motley collection of diesel shunters inherited by the UTA had the same style, although latterly ex-BCDR No. 28 was plain black, unlined. Numerals depended on ancestry: ex-NCC shunters had red plates as steam locos, while ex-BCDR stuff had painted numbers a la GNR.
On the NCC section, the numberplate backgrounds were also red, but the raised rims and numerals polished bare metal. This included the narrow gauge section, the rump of the B & L.
One "Jeep", I think it was No. 5, carried an experimental green livery, by all accounts like Isle of Man locos had in the late 60s, for a matter of months when new, before the then-new UTA decided it wouldn't wear well. Given how they looked after their steam locos cosmetically, it's probably just as well that such a light livery was given its marching orders.
Maybe Weshty might do a purpose-made set of transfers to cover over this awful error on the production model?