Hi Alice, I was told today that I should not use vitamin C or retinol from spring to autumn as I have the risk of hyperpigmentation.

Who told you that??! A good quality vitamin C and retinol will both help reduce hyperpigmentation, so keep on with them. You can read more about pigmentation issues here. What you DO need to do from spring to autumn is to be extra diligent with your sunscreen, and protecting your face from UV light as that is what will really kick off pigmentation in your skin.