I use 'at home' hair colour. Will colour containing sulphates damage a Brazilian blowout?

It is always best to colour your hair before the Brazilian blowdry as any colour is bad for it especially if it is lighter then your natural hair.
Leave it as long as you can, minimum 2 weeks but preferably longer and get a friend or even better a hairdresser to apply the colour being extremely careful to only colour the regrowth to minimise damage.
You can colour your hair the day before the Brazilian, your hairdresser should really of advised you.

Hi Dietz ,
As we are a Hair Extensions Salon its best you speak with the technician who applied the particular Straightening chemicals to your hair or a local Trichologist.
However it is logical that chemicals in excess are damaging to natural hair. To get insight into the severity you should speak with the Brazilian Straightening specialist who did your Blowout as they should have insight into the Chemical interactions .
Kind Regards
Management at Allure Hair Extensions

Don't do any home colouring as it will ruin your new Brazilian blow-out, and eventually it will dry out your hair.