Nail Varnish - Force

I bought this polish because I'm a huge fan of Illamasqua and I fell in love with this classic crayola blue. It looked great the first few times I wore it, the formula was great and it only took two coats for it to be completely opaque. However, after storing it for several months I found that it had changed into a dusty looking purple shade. I should mention that the polish was kept away from light and heat. I've heard from a few other people that they've also had this problem. This polish is too expensive to have this happen. Extremely disappointed!