Hi,
The color is working right but the problem is that, your PNG image have indexed colors.
So GD can't allocate a color which does not exist in the original image.
I have to check if I could bypass it without creating two images in the memory. But if you just upload the same image without color indexing, it should works fine.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.