I wouldn't concentrate too much on the names as if it isn't a shrimp expert selling them they could be anything so go by whether you like the colour/shade. For instance, dark blue wouldn't be good in a dark tank/substrate, the reds would be better, or a lighter blue if you want blue, and yellow would really be superb due to the contrast?
When I have seen them for sale here for example, blue dream are bright mid blue, blue velvet are dark blue (almost black) etc. Here is a link to a specialist site so that you can see what they should look like, they are as JayC states but it is easier to see than describe;
https://www.rendo-shrimp.de/epages/62701010.sf/de_DE/?ObjectPath=/Shops/62701010/Categories/Garnelen/Neocaridina_Arten/Blaue_Zuchtformen
Simon