Golden yellow booklets are for regular candidates. Mauve booklets are for candidates who have some kind of specific learning difficulty, which is marked on the front (dyslexia, for example). Blue sheets are for candidates who didn't turn up to the exam.
One of the exam scripts I had to mark this year was not golden yellow, though. It was a kind of greeny yellow.
I have no idea why this single candidate had their own, personal booklet colour. Maybe it's some cosmetic item you can pay for at the exam shop.
Oh, because I know you're interested: four candidates mis-spelled the word "lose" or a derivative and were marked accordingly. One spelled it wrongly three times in the same question, but I only counted it once.
The candidate who wrote "lossing" attracted my wrath but was spared punishment.