littleonefb - The Ipomoea purpurea that shows some degree of a blue,purple or pinkish star on a white background has been marketed by commercial companies as "Milky Way" or "Shiva"...the degree of intensity of the starring and the coloration can be affected by environmental factors like soil and overall weather conditions,especially temperature variations...genes for various pigments may also affect the way the gene for spotting shows up...

The name of "white Snowman" or just "Snowman" was used to describe a type where the color pigment was suppossed to be limited to just a roundish 'spot'...

The cultivars that will consistently display more blue or pink along with a consistent size/shape of the colored area will be difficult to isolate and to find.

I personally don't think there is any 'real' difference in the names that are being used to market these I.purpureas showing the gene for spotting...

The Ipomoea nil "Chocolate' and the 'Chocolate Silk' have another somewhat entangled history as the genes for any of the features displayed by one can be present or easily picked up from the other...similar to the Ipomoea purpureas,an almost infinite degree of merging of features can be encountered,confounding 'definitive' ID's...urban misconceptions about the nature of the coloration(s) displayed have added to the list of about 10 different features now attributed to variations on the 'Chocolates'...

The situation is similar to the Ipomoea purpureas mentioned above and that is any of the characteristics attributed to any of the 'Chocolates' can be carried or picked up from the other,so isolating and stabilizing any features can be difficult if not impossible...

The 'Chocolate' as pictured by the T&M catalog is rarely encountered and even the packets from T&M mostly produced variations on the 'Chocolate' theme...mutations from the "Rose Silk" offered by Park Seed,produced another range of 'Chocolate' variations...

Chocolates of various shades with and without a white outer edge,a darker inner star pattern,color streaking,various degrees of flat matte look or irridescence and the prescence or not of variegation in the leaves is often used to define the various 'Chocolates'...

I prefer to use a detailed description of what the plants I have display and to hopefully receive an accurate description of what another may have to offer for sale or trade...the features can be so overlapping that I personally find that exact definitions for either the 'regular' 'Chocolate' or the 'Chocolate Silk' may still be premature as of this point...someone else may have a different perspective...

Good Luck(!)...

P.S. I'm still working on trying to help/encourage in people an interest to tell the difference between the most common species(!)like Ipomoea purpurea,Ipomoea tricolor,Ipomoea nil and Ipomoea hederacea and a few others...there are so many honest mistakes on the web that just get copied and multiplied...and I think it is a very helpful tool to be able to tell the different species,before you can accurately tell the differences in the cultivars...the keys to ID the species are actually very easy(!),but people just think it is more complicated than it is,and get afraid to learn a few some simple features that would make alot more sense out of a perpetuating chaos...
Since different species will not naturally cross fertilize,knowing and growing different species would eliminate most concerns about unintended crosses...