Speccy game cases?

I know this may be a silly question to you veterans, but I am just building up my collection now after securing a zx spectrum. When looking at eBay listings I keep noticing how some have black cases (as shown in the photo) and some have a clear casing. Is this to do with the region or time of release?

I know this may be a silly question to you veterans, but I am just building up my collection now after securing a zx spectrum. When looking at eBay listings I keep noticing how some have black cases (as shown in the photo) and some have a clear casing. Is this to do with the region or time of release?