Hands up all those who think that the fan-heater person described by Simon would be one of those people.
Actually, I don't think he'd know what the plug was !
Your concern seems to be that if you use red accessories that this would be inappropriate because the voltage between the pins would be too low.
Then you haven't comprehended much of the discussion at all have you - because that is
NOT the concern
If you look at the table on the connectors specs/coding, you will see that the maximum phase-neutral voltage for a 5 pin blue plug/socket is 144V and phase-phase maximum is 250V. For a red connector these figures are 240V and 415V.
So, lets say we go with your argument that there will not be more than 240V present if we use a blue socket. Should someone find a bit of equipment with a matching plug, what's it's specs likely to be ? Phase-phase will be "safe" because there won't be any voltage between phases. But phase-neutral will be 240V for something that might be specced for only 144V - oops
It is true that the chances of someone finding such a piece of equipment are slim
- but they do exist and I've worked in environments with a 240V phase-phase voltage (in the UK and abroad).
But using a red socket, again there will be no phase-phase voltage - but the 240V phase-neutral will now be within the spec of 200-240V. Even though equipment with such a connector is more likely to be found, it shouldn't be damaged because it won't be exposed to a voltage above what it's designed for, and most likely "nothing will happen, it just doesn't work".
But to be honest I'd not be too worried either way - because as you say, it's not like it's some industrial complex with loads of 3 phase hand tools around.
I hadn't intended a long discussion on the merits of red and blue, I was only asking if anyone had ideas for connectors. I'm still thinking Klix 4 pin might be more appropriate