This is one of those cases where there are two hostas with the same name. One is registered and, therefore, the "official" version of H. 'Topaz' while the other is a non-registered plant and needs to be renamed to avoid further confusion.
 

This cultivar is the result of a cross of H. 'Neat Splash' × H. 'Dorset Blue' and is a sibling to H. 'Everlasting Love and Bliss'. It was registered by Greg Johnson of Iowa in 2004. The medium size hosta is 16 inches high by 33 inches wide with ovate leaves that have long, distinct tips. Its foliage is smooth textured and has thick substance. Pale purple flowers are borne from late July into August.

Hosta Helper will call this plant 'Topaz' (Greg Johnson).

According to The Hostapedia by Mark Zilis (2009), "The name 'Topaz' has also been used for a sport of 'Summer Music' from Alex Summers of Delaware..." It should be a medium size hosta with broadly ovated green foliage and pale lavender flowers that bloom in July.

Hosta Helper will call this plant 'Topaz' (Summers).

A miniature size, non-registered, green hosta originated by Wm Zumbar of Ohio was also known by this name according to Mark Zilis.

Hosta Helper will call this plant 'Topaz' (Zumbar).