Help with next colour

demi and permanent dyes are not longer lasting than semis. They fade in the exact way that semi's do but it is more noticeable in darker colors. you can make your semi dye last longer, i am sure there are threads that cover this topic.
The more damaged your hair is, the quicker demi dyes will fade and the more demi dyes you use, the more damage your hair will have.
you can get the same toning effect by using a violet shampoo than a damaging demi dye. 

demi and permanent dyes are not longer lasting than semis. They fade in the exact way that semi's do but it is more noticeable in darker colors. you can make your semi dye last longer, i am sure there are threads that cover this topic.
The more damaged your hair is, the quicker demi dyes will fade and the more demi dyes you use, the more damage your hair will have.
you can get the same toning effect by using a violet shampoo than a damaging demi dye.

I used to dye my hair with demi dyes and they definitely last longer than semi/ direct dyes. Semi/direct dyes only last a week for me. Two tops. I got one to last for 3 weeks with a pre color treatment and after color sealer but by then it was faded enough and my roots were grown out enough that it was noticeable. And I only wash my hair every 3 or 4 days with a color safe shampoo and luke warm water (I'm not washing with cold. It's almost winter. I do a cold rinse at the very end of my shower). I even tried making my own purple shampoo and conditioner with left over dye. I stopped dyeing my hair for over a year and my hairdresser says my hair is in very good condition.

I also have never seen any effect from a violet shampoo. I've even tried leaving them on my hair for a while. There is supposedly one Australian brand that is the best of the best but that's just what youtubers say and then that's ordering something from all the way over there that may or may not work.

Do you mean it lasts a week before it fades? Because if it’s lasting a week and coming out completely then it sounds a bit more like you’re not really putting it in correctly.

Colour safe shampoos are actually kind of useless. Washing your hair with cool or lukewarm water (it doesn’t have to be freezing, just not hot), but more importantly, using conditioner instead of shampoo (just scrub more than usual) works a million times better. I get virtually no fading for months if I do this.

I used to dye my hair with demi dyes and they definitely last longer than semi/ direct dyes. Semi/direct dyes only last a week for me. Two tops. I got one to last for 3 weeks with a pre color treatment and after color sealer but by then it was faded enough and my roots were grown out enough that it was noticeable. And I only wash my hair every 3 or 4 days with a color safe shampoo and luke warm water (I'm not washing with cold. It's almost winter. I do a cold rinse at the very end of my shower). I even tried making my own purple shampoo and conditioner with left over dye. I stopped dyeing my hair for over a year and my hairdresser says my hair is in very good condition.

I also have never seen any effect from a violet shampoo. I've even tried leaving them on my hair for a while. There is supposedly one Australian brand that is the best of the best but that's just what youtubers say and then that's ordering something from all the way over there that may or may not work.

If you used a pre color treatment then it was definitely not a semi/direct dye. You need to use direct dyes on clean shampood hair, no conditioner or any other products on the hair. The quickest i had one fade was one month when i used crazy colors which dont stick well on my hair.
Like Janine said, color safe shampoos arent great, you need to buy the ones that have no lathering agent and even then a little color still comes out. Osmo color mission is the best i have found so far and it still strips some color. As for the purple shampoo, you need one that is very highly pigmented. the ones on the highstreet shops are not well pigmented. Redken silvercharge is very good but a bit pricey.

Totally agreed with puerkz for what she said , Thank you for sharing the information