There may be reasons why a particular colour light main signal or position light shunting signal should be made more conspicuous than normal. This could be because of problems with misreading where signals are positioned alongside one another, or because the signal concerned has a history of being passed at 'danger'. The solution most commonly adopted, from 1994, was to fit a blue and white diagonally striped surround around the signal head. This primarily assists with close range viewing.