What should I do?

Naturally my hair is about a medium/dark brown, but It looks better when it's dyed a soft natural black. Ever since HS I have always used a temporary dye to get it darker. However, after about two weeks it begins to fade and get lighter. I want to keep my hair dark all the time, and I dislike having a few weeks of lighter hair and then having to color my whole head again each month. I am thinking about using a permanent dye and then just touching up the roots. What do you think is best for my hair? Dying it each month with temporary or doing it with permanent and then just touching up the roots? Need ideas/advice!

2a/2b, Medium Porosity, Medium Density, Lower Back Length, Growing out highlights.
Shampoo: SMMR Conditioner: SMMR or Organix Keratin Oil Leave In: Organix Shea Butter DC: Coconut oil, Olive Oil, Jojoba oil mixed all together with v05 conditioner.
“Imperfection is beauty.”
― Marilyn Monroe
Shampoo: SMMR Conditioner: SMMR or Organix Keratin Oil Leave In: Organix Shea Butter DC: Coconut oil, Olive Oil, Jojoba oil mixed all together with v05 conditioner.
“Imperfection is beauty.”
― Marilyn Monroe
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Comments
The advantage of temporary dye is if you get fed up with it and it's definitely a wash out dye then you can dye it another colour. Even though most temporary dyes aren't that temporary and do stain your hair you are still able to dye over them with some colours.
If you use permanent dye even though the dye has faded due to the dark colour you would either have to strip your hair, which is damaging, or cut it off if you want to change the colour.
To reduce fade use cool water only and reduce water exposure - leave in instead of rinse out conditioner, stretch washes with dry shampoo.
Permanent dye is always damaging due to the alkaline chemicals/ peroxide (yes even in dark shades), this can be reduced with hydrolysed protein (wheat or soy) and/ or coconut oil treatments.
CO-wash: Inecto coconut/ Elvive Volume Collagen
Treatments: Komaza Care Matani, coconut/ sweet almond/ fractionated coconut oils, Hairveda Sitrinillah
Leave in: Fructis Sleek & Shine (old), Gliss Ultimate Volume, various Elvive
Styler: Umberto Giannini jelly, Au Naturale styling gelee
Flour sack towel, pixie diffuse or air dry.
Experimenting with: benign neglect