I really love the colour of this one. It's mesmerising as it fizzes with bright blues and greens pouring out. Beware though, these can stain your skin or hair temporarily if you come into contact with the undissolved chunks. If having random blue spots for a day or so is a worry you could always wait until the bath bomb has fully dissolved before you get in.
$7.99 from Bath Box
Summary Gorgeous colours to liven up your bath but be careful you don't get Smurf Pox.