Since I wasn't sure how dark the dye would be, I decided to only do the under layers of my hair just in case it was too much. Remember, I don't often stray too far from my usual midlength highlighted brown hair.
Before applying the dye, I wet the section I wanted to colour, then towel-dried it. (You can't totally tell here, but my hair is damp.) I chose to go with the Good Dye Young I'm Bored Temporary Hair Colour Serum in shade Binge Watch (£10).