You need a salon treatment when you colour your hair, or when your hair is dry and dull. If your at-home treatment isn’t working like it used to, you should speak to your stylist to see what they can do for your hair.
After colouring, I usually get a Goldwell Vivecap treatment which is a leave-in treatment that helps lock in the colour so that it lasts longer. These only take a minute to apply at the basin and are left in your hair. They’re not expensive (price varies at different salons) but if you’re spending a lot on your colour, add this to help it last and look its best.