Nothing but if you've lived in the UK long enough, you either love or hate the slab boring varieties of red bricks. Ultimately i dislike them but there is a comforting reassurance that most people regardless of social class has a house made out of these dull red bricks.
Most of the UK houses are old so im guessing it was simply down to access to materials or some other reason, nowadays new houses do have a little more variety but there are still very few colourful buildings.
Having been abroad to cities like Lisbon, Istanbul or Copenhagen. One of the most memorable aspects of these cities is their colour variety. Im sure there are good reasons like maintainance as to why it would be impractical for the UK (rainy country) but there is something very appealing to seeing colour all around you.