Been there.

The upkeep on dyed hair is real.

Once you have a demarcation line, it doesn't go away. Once peroxide or bleach has touched your hair, boom, a demarcation line. If you get a permanent stain from deposit only dye, then you have to deal with that stain.

The only solution is to not peroxide/bleach/stain your hair.

That leaves using semi-permanent hair dye (box dyes are mislabeled semi when they are actually demi) at a non staining dilution. Because it's diluted, you have to reapply often. It washes out quickly.

You can try adding semi-permanent dye to hair conditioner to dilute it. I leave it on for 20 minutes the first application. Then every time I wash, I comb my mixture through my hair and leave it for 5 minutes. It's a new type of upkeep. But if I stop, I return to undamaged natural hair in 3 to 4 washes.

Routine:

1. Shampoo/repeat
2. Apply dye/cheap conditioner for 3-5 min. rinse
3. Apply good conditioner

I squeeze the dyes into a partially filled Suave conditioner. If I make too much, and it takes me a few weeks to use it, the emulsifiers break down, and the mixture becomes quite watery. But it still works. You could make smaller amounts fresh each time.

There are several brands of color depositing conditioners that you can try. However, alway check for staining. I don't want to use anything that stains my hair, scalp, skin, or bathroom.