I like the green hair. I'm guessing Katy just had the tips of her hair done so she could do more with it like tie it back like she has in recent photos.
I only clicked on as to why Katy's hair has orange tips in the Birthday Lyric video the other day. If anyone has dyed their hair funky colours before you'll know there's a set of colours your hair sometimes has to go through before being the colour you want. It's extremely difficult to dye black hair any other colour (as you can imagine) and bleach will send it orange in the first stage!
I've experienced it myself!