Katy Perry kicked off her Prismatic World Tour in Belfast, Northern Ireland on Wednesday, and on Thursday Lady Gaga tweeted a jab at the singer when she wrote, "It looks like green hair and mechanical horses are the thing now."

During her show Katy rides a mechanical horse, and as you all know, the pop star recently dyed her hair bright green. Gaga apparently took offense to this as she recently colored her tresses green as well, and as for the horse reference, Gaga arrived at the AMAs last year on a giant mechanical steed. As far as we can tell, she hasn't used one as a prop onstage and uh, HOW many times has Gaga changed her hair over the years? From Kelly Osbourne to Kylie Jenner, at any given week any celeb could be accused of stealing her hair color, so we call BS on that.

And this isn't the first time Gaga has said something nasty about Katy! Two months ago Mother Monster performed at the Austin Convention Center and told the crowd, "I don't know what the f*ck all I have to do with Katy Perry Our music is so completely different. I couldn't be more different, really."

After that happened, Gaga tried to sweep it under the rug when she told Ryan Seacrest their was no feud, adding, "I really like Katy Perry and I like her fans."

But is she telling the truth? Seems like she has it out for the "Roar" singer!