Why do these two tablets have slightly different model numbers?

[TwistedHelixis]

Been looking at getting a Samsung Tab A 8 inch. Found one on Amazon and one at John Lewis, both for the same price but they have different model numbers and I cant find out why.

 

SM-T290NZKABTU

 

SM-T290NZSABTU

 

I assume the K / S differences must mean something, any ideas.

[mavhc]

black vs silver colour