The couple I invited over went to the Lake District yesterday with some friends from India.
When they got back to their house in Worcester, the two Indian men went into their lounge with their muddy shoes on, spreading mud on the lovely light carpet. They were apparently apologetic and cleaned up.
This seems a fascinating story given that Indians generally do not wear shoes in home (I know it varies and the custom is stronger in southern India than northern India).
Maybe they assumed that because white folks wear shoes in the house, they do not worry about mud.
Perhaps the moral of this is that if you want people to take their shoes off when they are muddy, it is better to get them to always take their shoes off in case they forget when their shoes are really dirty.