Most Numatic cleaners were available in at least four colours. The fact of the matter was that Numatic chose to showcase Henry in red, George in green, Basil in yellow, and Charles in blue, and these combinations are what most independent retailers stocked, but they could have chosen to order in any colour available.
When Numatic began to supply the major high-street retailers, the colour combinations remained the same. Frankly, I don't know why Numatic even bother with a colour choice as consumers probably don't care. Everyone seems to think Henry is red and that a different colour means a different type of Henry, and so on.