Francesca sent in her solution:

As 1/12 of the discs are blue and this is a whole number, the total number of discs is divisible by 12. Also, the booklet is square, so the possible numbers of discs are 99, 95, 91, 84, 75, 64, 51, 36, 19.

Of these, only 36 and 84 are divisible by 12. But 36 doesn't work, because then 36/2=18 discs would be red. Also, the booklet would be 8x8, so the short rows would be 2 long, so we'd have to have 2+2+10 x something = 18 and this doesn't work.

So there must be 84 discs. Now 42 are red, 21 are black, and 7 are blue. So 3 are green, 6 are orange, 1 is white, and 4 are yellow. So 6/84=1/14 of the discs are orange, 3/84=1/28 of the discs are green, 4/84=1/21 of the discs are yellow, and 1/84 of the discs are white.