Obviously 230V isn't an issue, but 110VAC is sometimes used here on building sites and in some industrial situations. It's supplied by a centre tapped (single phase), or a star connected (three phase) transformer/generator, so both conductors are 55V, or 63.5V, with respect to earth. I haven't seen what wire colours are used in 110V fixed installations, but appliances use ordinary flexible mains cable, with brown, blue and green/yellow conductors. I would hope 110V wiring is marked and kept separate from 230V/400V, irrespective of the colour code used.
I've seen those building site transformers and always thought it seemed like a good idea, at least prior to the development of GFCI/RCD protection. I have no idea what they use for color coding
Even with RCDs they're a great safety advantage. RCDs are meant to provide protection in the unlikely even of a shock - reduced low voltage supplies are used where physical damage and unfavourable conditions (wet ones.) are significantly more likely than normal.
For colour coding, technically you would use two browns (remembering it's single phase so there's no polarity, and there's no neutral), but realistically they use exactly the same materials as everything else (kind of the point, really), so it's all brown and blue.
I didn't realise they also have them in the US.
I'm not a fan. They were good back in the days before RCDs, but nowdays the manual handling hazard of lifting heavy transformers and the fact that 55VAC, or 63.5VAC can still deliver a considerable shock, make plain old 230V + an RCD a safer option.
I agree that if you add an RCD, 110V is safer than 230V, but I've not seen that before. If a place wants reduced voltage, they should add fixed wiring and a centralised transformer, or generator and RCDs, rather than those back breaking transformers.