I never did remember what the different colours on squash balls meant, but found a handy guide on Wikipedia…
Different balls are provided for varying temperature and atmospheric conditions and standards of play: more experienced players use slow balls that have less bounce than those used by less experienced players (slower balls tend to ‘die’ in court corners, rather than ‘standing up’ to allow easier shots).
|Orange||Super Slow||Super Low|
|Double Yellow||Slow||Very Low|
|Green or White||Medium/Slow||Average|