Ice Goth, or negative Goth, is perhaps more a way of playing with Goth fashion than a style subset - it's a style of Goth fashion that utilises white clothing instead of the traditional black, and is used more often for a single outfit than a person's entire wardrobe.
If I had to hazard a guess, I would say that the inspiration for this look came from the whimsical nature inherent in the Goth subculture - Goth fashion is intended to be creative, fun and a little rebellious, so why should it not break its own 'rules'?
Back in the 80s and 90s, some young Goth women wore antique wedding dresses with their heavy boots, big hair, dramatic make-up and leather jackets; white, flowing gowns have always been popular for a 'Bride of Dracula' effect, especially following the release of Tim Burton's Corpse Bride. Lolita fashions have long since used white as a predominant colour, as white creates a delicate, innocent effect - highly ironic, since a white gown or veil also invokes images of the traditional burial shroud... White can be ethereal and fairylike, innocent, regal, sexy (for example a fetishistic 'nurse' outfit for the club) or a bit creepy - perfect connotations for the fashion-conscious Gothling who fancies a change.
Of course, all-white clothing is considerably less practical than the usual black - perhaps recommended for special events (or times when you're not likely to get wet, sweaty or venture near dirt). Having said that, white outfits are becoming more commonly seen at Goth festivals - it certainly makes one stand out amongst all that black.
If you don't quite dare to wear an all-white outfit but would enjoy the contrast, white accessories such as tights (white lace tights or fishnets would look yummy), lace or velvet chokers, parasols, bags, spiked wristbands, gloves and even white contact lenses are easily available. New Rocks are even available in white if you wanted to go the whole hog (or are thinking of getting married).
White lipstick, often worn with black liner, is sometimes seen, although white eye make-up is difficult to pull off if you have pale skin (Goths of colour would look stunning in white clothing and make-up). White or platinum blonde hair is used to contrast with black clothing but could look equally drop dead paired with white for an otherworldly look.