The amount of products that will permanently stain your carpet are small, but I have highlighted the big 3 to avoid.
1) Soda drinks with food dye, normally red cola or vimto, these pop drinks have food colouring that can instantly dye your wool carpet, you could save your carpet if you react straight away but I would call us out straight away.
2) Indian foods such as Massalas, curries can instantly and permanently dye your carpet on impact, that’s how strong these dyes are, so be very careful the next time you order your take-
3) Pet urine is a little easier if you react immediately, however if left unattended for 24 hours or so the chemical reaction would already have taken place and it will not come out.
*3 to avoid at all costs.