So, the old contractors (God bless em) left £100’s worth of mortar out in the rain.  When I went to the manufacturer to get some more, I was told that they had run out and were not making it anymore.  The search for a new mortar which was the same colour then began.  The problem is, you can’t tell what colour it is until 4-6 days later when it has dried.  Hence, I had to make up rather a large number of samples.  The final recipe was 45gms of black and brown dye to 25kgs of 3xno.21 type lime mortar.