Only seeing this now.
UTA uniforms were a colour which was either loiterally black, or a grey so very dark that it was to all intents and purposes black. Shirts were white.
Caps were black, and carried a green-background UTA roundel on them prior to 1960, and in many cases long after that; the full crest was introduced as far as I remember in 1960, but I never remember seeing caps with that on them - though it spread to locos, coaches, railcars and published material pretty quickly.
I also remember some UTA uniforms had a green lining of some sort, like the later NIR ones had in maroon, but I don't fully recall the details.
For a 00 scale sized model, lining in uniforms won't apply! So, black uniform and cap and white shirt. Drivers in a sort of faded blue overalls on steam, normal uniform on diesel. Drivers caps were shiny-topped.
Hope that helps.
JB