Also known as Siberian or Russian winter white hamsters. These hamsters change colour in winter to white so it is easier to hide in the wild. They come in 3 main colours, pearl (white) which do not change in winter, natural (mucky brown, their original colour) and sapphire (a grey/blue).
Most pet shops sell the Russian hybrid hamsters that can often be mistaken for Djungarian hams. You can tell they are winter whites if they change colour in winter, or by their head shape.