Notice what is left behind
A flat colour change after a spot can be post-inflammatory hyperpigmentation. A change in the surface, such as an indentation, may be a scar. Pigment and scarring can occur together and may need different approaches.
Reduce the sources of irritation you can identify
Picking and using several irritating products can make it harder for your skin to settle. If breakouts are ongoing, ask a pharmacist or GP about treating the acne as well as discussing the marks it leaves.
Look at the sunscreen label
Use broad-spectrum protection with SPF 30 or higher. Tinted sunscreens with iron oxides can also help protect against visible light, which can contribute to pigmentation. Choose something you tolerate and can use consistently.