[Question] What do the different covers for the manga mean?

[hideincarnate.livejournal.com]

Hello everyone! Please excuse me for asking an obviously stupid question but I am in need of your assistance.

We all know volume 3 of the manga is out and that's great! But apparently there is also an illustration book as well? They have the same covers but the background is a different color...

So my question is: is this how it is for ALL the manga volumes?

I'm looking at amazon.co.jp and I see five different manga volumes. 1 for volume 1, 2 for volume 2, and 2 for volume 3.

Volume 2 and volume 3 both have a book that says 特装版, which to me, just means "special edition." But does this mean these are illustration books or just collectible covers? Volume 2 is green but the special one is brown, Volume 3 is pink and the special one is white.

I'd love to buy the illustration books as well as the manga, but if it's just a difference in covers, I wouldn't need two copies...

And if these are illustration books, where can we get them? Because it looks like they're only up for sale used on amazon.co.jp and I don't think we can buy things used if we don't live in Japan...

Any help would appreciated guys! I'm sorry for being such a loser at all this. OTL