CasioG-Shock G-SHOCK Funk Men's Watch GW-7900-1ER

What is the difference between this model and this gw-7900b-1er?

Would it change time automatically in different time zone. let say i'm flying from uk to us? also, will it move 1 h back on spring?

Is it normal that the screen goes blank? It only happens in the evening when i am not using it (then it works). Battery indicates it is still full.

Just received my watch. The colour is slightly more grey than deep black. Is this normal?