These are water based liquid dyes that are supplied in a concentrated form so we would recommend testing a small quantity first to achieve the colour required. If necessary they can be diluted further with deionised water.
All colours can be mixed to create other colour combinations so have a go and create some variations of your own.
It is actually quite difficult to achieve a vivid colour in a bath bomb as you are starting with a white base so don't be tempted to add too much as when the bath bomb hits the water it will turn the water a very deep colour.
We always recommend water based dyes over pigments for bath bombs.
However, we would always recommend testing a small amount with your formulation before starting any large scale production.