Why is it called the Purple Sapphire, when it is yellow?

Why is it called the Purple Sapphire, when it is yellow? I have taken many pictures of this lovely little butterfly....which seems to be yellow and red and brown.....

Well, last week I finally came across this lovely one., with its wings out in the sun, and all was clear...

Note the use of fill flash in the image below, which I think crispens up the image and allows me to shoot at 160iso and not 2,000

This species of butterfly exhibits slight sexual dimorphism where the males have a purplish blue patch on the dorsal side of the forewing while the females do not.