A surprisingly high number of players have difficulty in distinguishing between coloured balls and clips –  red, green and brown is the common difficulty.  The technical term is Colour Vision Deficiency (CVD) or Colour Blindness.  The CA now recommend:

(a) Brighter colours should be used when repainting clips and in particular, adding a white dot to green clips and diagonal white stripe to brown clips.

(b) It is now permissible to ask opponents about the colour and position of clips in a game.

(c) When using GC scoring clips use Yellow for a Red/Yellow side and only have one of green or brown in use when the Green/Brown side are playing.

(d) Team captains ands tournament managers should allocate 1st colour balls whenever possible to any player who has CVD.

Here is the full recommendation:

CA Report – Helping Players with Colour Vision Problems.