Border resized images

-- HikaShop version -- : 3.0.1
-- Joomla version -- : 3.6.5
-- PHP version -- : 5.5.37
-- Browser(s) name and version -- : Chrome

(This is a testsite)
While adding pictures to the products, during upload they are resized and a white 'border' is added to fit the configuration, category page 200 x 200 px and productpage 400 x 400.
As not all the images are the same size, I can't adjust the setting differently.

I can't find this in CSS with help of Firebug, so I assume it is done during uploading/resizing. Is there an option to change the white into transparent or the background color of the pages?

Thank you, exactly what we needed!