Always apply colour at least 48 hours after a treatment, as colour can lift. The treatment is partly working with the sulfate bonds, which sits under colour pigmentation. If you were to colour your hair before, the treatment could lift that pigmentation. The recommendation is to book Nice and Smooth into your colour cycle, getting a Nice and Smooth 3 weeks before their colour, every other colour cycle (every 12 weeks). Your colour will pop even more as the layer it sits on has been treated.