(Applied on Brown - colour remains the same and covers grey hair)
2N can be used on the following colours to achieve a dark tone colour:
3N - 4N - 5N - 6N - 7N - 4D - 5D - 7D - 4M - 5M - 7M - 4R - 7R - 7C

2N - Brown with 5% grey hair
If grey hair is all over the head, you can use 4D, this will create highlights on the grey hair and Dark Golden Chestnut on the rest of the hair. On more than 5% you must use this formula.
2N - Brown with 10% - 20% grey hair
Mix 25ml of 2N, 35ml of 4D, 60 ml of glycol to get a Dark Golden Chestnut.

2N - Brown with 30% - 50% grey hair
Mix 30ml of 2N, 3Oml of 4D, 60ml of glycol to get a Dark Golden Chestnut.

2N - Brown with 60% - 100% grey hair Mix 45ml of 2N, 15ml of 4D, 60ml of glycol to get a Dark Golden Chestnut.

This formula will apply for 2N brown to be mixed with 4D (Golden Chestnut), 4M (Mahogany Chestnut) and 4R (Copper Chestnut), 4C (Ash Chestnut).