How soon can you put a semi colour over a permanent?

You can typically apply a semi-permanent color over a permanent color immediately after rinsing out the permanent color, as long as the hair is in good condition and not overly damaged. However, it's advisable to wait at least a week to allow the cuticle to settle and reduce potential damage. Always perform a strand test to check for any adverse reactions and to see how the semi-permanent color interacts with the existing permanent color.