Each time you pass a grading assessment your Grading Book is marked against each kyu grade as:-

I for an intermediate grade.
F for a full grade.

The correct belt colour to wear for each grade is as below.

9th Kyu I = white belt & 1 red strip.
9th Kyu F = white belt & 2 red stripes.
8th Kyu I = white belt & 3 red stripes.
8th Kyu F = white belt & 4 red stripes.
7th Kyu I = yellow belt.
7th Kyu F = yellow belt & 1 red strip.
6th Kyu I = green belt.
6th Kyu F = green belt & I red strip.
5th Kyu I = purple belt
5th Kyu F = purple belt & 1 red strip.
4th Kyu I = purple belt & 2 red stripes.
4th Kyu F = purple belt & 3 red stripes.
3rd Kyu I = brown belt.
3rd Kyu F = brown belt & 1 red strip.
2nd Kyu I = brown belt & 2 red stripes.
2nd Kyu F = brown belt & 3 red stripes.
1st Kyu I = brown belt & 1 black strip.
1st Kyu F = brown belt & 2 black stripes.

1ST DAN = BLACK BELT