For now, yes- this is it. Not sure if Tateno sensei will continue the series. We'll ask tho. We haven't decided if we'll license this: http://ow.ly/4UOou which is the tanko version of Yellow 2 Ep 1~3. ..Still thinking about it..
Yellow 2 was collected (all three chapter) into a tankoban in Japan, called Yellow R (R for returns). I'm going to guess it will get licensed in the next year or so for all the people who either didn't want to buy the individual chapters, or didn't get a chance to.