Answer: A Monet painting
At the party that Christian and Cher went to on their date, Cher and Tai saw Elton dancing with Amber. Tai got upset, because Cher had wanted to fix her up with Elton, so Cher told Tai that Amber was a "full-on Monet", meaning that she looked fine from far away but was a big mess up close. To confirm, Cher asked Christian's opinion and he peered at Amber and simply said, "Hagsville".