only buy at reputable shop, or authorized yonex dealer, there's no way you can judge by holding fake and real packages side by side, even with 3D logo, i'd experienced it , my buddy, who own a badminton store showed me both fake and real strings, racquets,... just can't tell the different.
Asia has a much larger selection of string colors as there is enough demand to justify them. for other regions, local distributors are more conservative when they bring in string colors as they don't want to be stuck with thousands of colored strings in their warehouses.
having said that, there are times when i see certain color string getting more stock in retailers in HK and i wonder if that's because Sunrise has over-inventory of those colors and dumping them to the retailers.
It may be not easy at all to identify fake strings if you dont touch them.
I usually can identify them by the texture, but even then I am not very sure (with BG80 was easy so far, but I admit that plain surface strings are difficult).
About the colors you can check if that color is referred in the brand website.
If you are terribly suspicious you can ask the region wholesale distributor if that retailer is authorized and if that specific string model and color was supplied to him.
If the price is too low then you may have another clue.
The safest way: buy non-yonex strings (buy from other reputable brands, not "crap" brands), I do that many times, save money most of the time, I am certain that it is genuine and the clients play with them as well without complaints.