I have found in my workshop a full reel of 3 core and earth of the previous colour regime. I believe this can no longer be used but it seems a bit daft to me. e.g. If you were to do a 3 way light switching using an intermediate switch and 2 two way apart from the brown most of the terminations in the switches would be sleeved. I worked out there would be 9 sleeved terminations. So what would be the problem of using the old colour and putting brown sleeves on the red?