Painting houses like this is quite common in Wales, near the sea particularly. See places like Tenby. Bristol being very close to Wales means it does have more cultural crossover than the rest of the UK, I wonder if that has anything to do with it.
Tobermory, on Mull in Scotland, is a well known (UK) example of colourful houses - it is shoreside too. It's probably that in most tightly packed housing there's no vista, only on the shore does that become possible and so the use of colour enhances the visual amenity.
By which I mean, the Mediterranean coast has loads of colourful seaside towns The Amalfi coast (see Vernazza for an amazing example, or the other four Cinque Terre, or Pixar's Luca for a well-observed only slightly exaggerated version), Menton in France is very colourful, Venice has very colourful bits…
Roman houses, much like their now-white statues, were very colourful, so I suspect they spread their love of coloured plaster wherever they settled. Though I am not an historian (IANAH).
Painting houses like this is quite common in Wales, near the sea particularly. See places like Tenby. Bristol being very close to Wales means it does have more cultural crossover than the rest of the UK, I wonder if that has anything to do with it.