I haven’t done DIY in a while but my general advice for preserving vibrant color:
* use only color depositing products, shampoo and conditioner, because every time you wash your hair you’re going to be stripping color. Find one that’s closest in tone and warmth to the tones of your hair. You want the conditioner to be as saturated in pigment as possible so look for one that’s very rich in color. When I would bleach my own hair I used to apply purple conditioner to dry hair so that it wasn’t diluted by water and leave it on for a long time like a mask, then rinse it out and shampoo—if you do this try to make sure the product you use doesn’t have any drying alcohols and that it has a nourishing consistency
* avoid silicones and sulfates if possible
* if you used something like manic panic you can mix the exact color you used with conditioner and use that
* wash your hair as infrequently as possible and with the coolest temperature possible
* air dry and avoid heat styling as much as possible! If you need to heat style for a special event use heat protectants and don’t apply heat directly to the hair for too long
* protect your hair with a bonnet or scarf when you sleep—this will protect your pillowcase from any potential color transfer too because if you’re regularly depositing pigment into the strands they may leach out if you sweat in the night
* try to be mindful of direct sun exposure because that can also cause fading—you can buy UV protectant for your hair!! I used to use Fekkai Pre-Soleil mist