As a short term measure until you get a new radiator plain water is perfectly fine and will do not the slightest harm to your cooling system. The coloured coolant you refer to is a mixture of water, anti-freeze (ethylene glycol), dye, and a corrosion inhibitor. The anti-freeze component is in it for obvious reasons; the corrosion inhibitor is essential for long term use to prevent the electrolytic corrosion which occurs between the different metals in the cooling system, (aluminium, copper, steel, zinc.)
Whether the repair will survive a 400 mile round trip is unknown. It really depends what sort of sealant was used, how big the hole was, and whether that part of the radiator is under enough stress to open up the repair. What concerns me equally is the thought of all that sealant circulating round the cooling system. I don't know if modern sealants are any better, but at one time there was a fear of it clogging up the narrower water passages in the system.
In your position I would certainly not trust the car for anything more than a few miles at a time on non-essential journeys. Get the train instead.