i used to work as Nippon paint's colour consultant and yes paint do gets bad.
they shld be using the same can of paint and u can ask them to show u the can of paint or you can bring the colour chart and compare it nx to the wall-it shld look the same IF it's the same colour. I am sure that sthing is wrong with the paint and even with the 2nd coat, it shldn't looked differently. of cos only that the colour will look more obvious and evenly.
Pls ask ur painter to repaint it...