Whenever I have a pre pig situation I always use the same method and it has never let me down. This also works on the most knackered of hair.
Spray the entire head with a porosity balancer and dry it in. Choose the correct pre-pig shade. nixxxminxx39 was spot on with her levels. I use a mousse. I actually don't like indola as they have metallic salts in them. I use Schwarzkopf.
Then go in with your target shade, with a touch of target base and 3%.
Once the have got a decent shampoo, my clients colour normally stays at least 6 weeks.