Which one should go first: keratin treatment or coloring?
A better option is to color your hair, then enrich it with keratin. Keratin straightening procedure will help you retain your color for a longer time as it wraps the highlights as well as a permanent and semi-permanent color well.
If you decided to go ahead with the keratin treatment first, it is better to schedule coloring at least two weeks after the procedure.
Can keratin treatment be applied after the chemicals or relaxers have been used?
Luckily, you can do it. In fact, keratin treatment works great for the hair that has already been processed with relaxers, Japanese or Brazilian straighteners, perms, etc. Keratin treatment consists of the natural ingredients that restore the health of your hair and remove frizz, at the same time making it shiny, smooth and vibrant. Do remember to schedule a keratin treatment two weeks after applying chemicals, though.
Stay Healthy, Stay Beautiful, Stay Trendy, Stay Stella.