The colour change has been controversial and was delayed for three decades, because the colour blue which was previously used as a phase colour is now the colour for neutral, and the colour black which was previously used for neutral indicates now a phase. While confusion between these conductors could be dangerous, the combinations of colours used usually resolves ambiguities. It has also been suggested that the new phase colours are difficult to distinguish in low-light conditions, but the same can be claimed for most colour combinations, including the old British phase colours. A mnemonic advantage of the new colours is that the first two letters of "brown" and "blue" match the corresponding positions on the socket face: "bottom right" and "bottom left".