Hair can be dyed any color after being bleached according to Clairol. When a blonde dye is added to hair that has bleach highlights, the bleached sections might have a slightly different shade from the rest of the hair.
Bleach removes the natural pigments from within the hair shaft. When hair is dyed after bleaching, the dye fills the hair shaft more readily, giving it a more robust color.
With bleach highlights, the highlighted part of the hair will absorb more of the dye than the rest of the hair. This would leave the hair with varying shades of the dye being used, leading to natural highlights in that color.