Your English speaking hairdresser in Buenos aires understands colour, I added the pH chart to highlight something IMPORTANT. The neutral pH is 7 yet the the protein keratin which makes up your hair is best in a slightly acidic state, it keeps the cuticles nicely closed and promotes shine. Blonde hair, if it goes too far it turns to cystaic acid (think of wet cotton wool, not great on your head, and irreparable)
Here is a popular question:
I lightened my brown hair but want my natural colour back. Can I darken it with a home colour kit?
It's not as easy as slapping on some brown dye, but with these pointers, you can get your natural colour back. One of the basics you learn when studying the chemistry of hair is that when you bleach your tresses, you strip away the rainbow of tones (bits of red, orange, yellow, and blue) that make up a rich brown hair colour. So you have to put those colors back in to re-create the original colour, this is why when you place a "natural" brown onto prelightened hair it often looks GREEN, there needs to be enough RED PIGMENT in the colour to counter the green. To do this, pick out a semipermanent hair-colour kit in a warm brown shade (look for the word golden in the shade name). Let the colour process for as long as the directions indicate, then rinse out. After your hair dries, apply another semipermanent dye that matches your roots exactly. This should bring you back to your beautiful natural hue.
Your English speaking hairdresser loves home hair kits, they are great for business.