Instagram to share a snap bowls of multicoloured sponge cake mix. Holly showed off a yellow, blue and red bowl, as well as one that was missing its green dye.The star told her fans about her baking mission, writing: "Rainbow cake incoming."And her followers were excited about seeing the result.One wrote: "Post a photo when it’s finished please.""Looking forward to seeing the finished cake," another wrote.A third added: "Hopefully you will post the finished product.....