Natural Remaining Pigment

NRP is the tonal value that the hair contributes as it lightens. 

10: lightest blonde----pale yellow

9: very light blonde----yellow

8: light blonde----yellow/orange

7: medium blonde----orange

6: dark blonde----red/orange

5: lightest brown----red

4: light brown----red

3: medium brown----red

2: dark brown----red

1: black----red