This is video of when I dyed my hair blue, pink, and purple. I used emerald and pink Splat hair dye, usually around $9.00-$12.00. You can mix the dyes to create a third color
I always leave in color dyes longer than the recommended time, these dyes wont do much damage to your hair so it doesnt really matter. However, don't leave bleach or black/brown dyes in longer.
Also, if your hair is anything darker than light brown, you will need to bleach your hair first.
When bleaching hair, I recommend lathering tea tree oil or coconut oil on your hair first. Leave it on while the bleach is in your hair, it helps to protect against damage. Your hair will likely still receive damage, just not as much as if you were to bleach your hair normally.
If you are going to bleach and then dye your hair, wait at least one day after bleaching before you dye your hair. If youve bleached your hair more than twice, wait at least a month. Nobody tells you this but if youve bleached your hair too much and do not wait to dye it, the dye will not take to your hair and will likely wash completely off.
Your hair does not have to be super blonde or white for this dye to work. Splat and a few other dyes will look great on hair from white to medium brown. White hair to light brown hair will turn out the same color if dyed. Medium brown will be darker, if your hair is dark brown this dye will only tint it. I would suggest getting to a dark blonde, almost brown before dyeing bright colors.
Other amazing dyes I have used are Beyond The Zone and Ion. If dyeing with Ion youll need light blonde hair. Many people use Manic Panic and I advise against it. Ive dyed my hair with their red and it turned orange, my hair was white. I also used blue and it came out green. I dont know if this is just me but yeah.
Anyways, if you have any questions feel free to ask me! Ive been dyeing my hair since I was about 12, but Im not a professional.