This is a Fenton Art Glass vase in a color called Periwinkle. It is a heat sensitive glass and looks like slag glass with the variations in the shading. This is a melon vase, and as you can see the interior is ribbed. It stands 5 inches tall. The actual color of this vase is darker and brighter than the pictures show. Fenton first made Periwinkle in the mid-1930's. They brought it back in 2004 and it was a big hit.
I don't see this vase pictured in my reference book; perhaps it was a sample. There is no Fenton logo on the bottom.