Wiring colour codes
The standard wiring colours in the UK are (as of 2006) the same as elsewhere in Europe and Australia and follow international standard IEC 60446. This colour scheme had already been introduced for appliance flexes in the UK in the early 1970s, however the IEE recommended for fixed wiring until 2006 a different scheme. As a result, the international standard blue/brown scheme is as of 2006 found in all but the oldest appliance flexes. In fixed wiring, the blue/brown scheme is only found in very new (post-2004) installations, and electricians are likely to encounter the old IEE black/red scheme in existing installations for many more decades.
Current IEC Protective earth (PE) Green/yellow striped Neutral (N) Blue Single phase: Live (L) Three phase: L1 Brown Three phase: L2 Black Three phase: L3 Grey
The standard colours in fixed wiring were harmonized in 2004 with the regulations in other European countries and the international IEC 60446 standard. For a transitional period (April 2004 – March 2006) either set of colours were allowed (but not both), provided that any changes in the colour scheme are clearly labelled. From April 2006, only the new colours should be used for any new wiring.
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 now indicates a phase. While confusion in identification of these conductors could be dangerous, the combinations of colours used usually resolves ambiguities. The installation of cables with the 'new' colours in an installation where the 'old' colours exist, could leave the way open for confusion; it is important in such situations that consideration is given to correct identification of the cables – with the use of marker tags if necessary. 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 "BLue" and "BRown" match the corresponding positions on the BS 1363 socket face: "bottom left" (neutral) and "bottom right" (live).
Lifted from wikipedia