Can I mix the FRAMCOLOR PURE PIGMENTS PLUS shades to obtain different tonalities?

Yes, you can mix the shades together bearing in mind that the reds are vibrant and will dominate the formulas. For instance, FRAMCOLOR PURE PIGMENTS PLUS /46 (Amber) can be added to dilute the vibrancy of any of the reds at a 3:1 mix ratio (3 parts /46 to 1 part /55).