Firstly what you should consider is your skintone!
If your skin has yellow undertones (warm), it's best to choose warmer colors; if your skin has pink undertones (cool), go with cooler colors.
Remember: If your hair is dark to begin with, the colour won’t show.
You'll have to bleach the parts of your hair you want to dye a certain unnatural color. And bleach will damage your hair (the more it stays on the more damaging it will be - the stronger it is the more damaging it will be > hopefully you're one of the lucky people whose hair takes faster to the bleach xD)
Whatever happens remember your color wheel:
Example: If your hair is initially yellow (as it tends to go after bleaching) - if you dye it red it will turn out orange.
P.S. You can try taking inspiration from flower colors. =)
Would you try it?
Have you already tried it?
Were you satisfied?