I have a few CT poplins. I always wear an undershirt with them, but I generally think they are fine. Poplin is supposed to be the finest, smoothest shirt fabric, and are inherently thin. It doesn't mean they are poor quality.
As for the blue color, I did find a very pale blue poplin about a year ago. I love this shirt and would like to get more, but I haven't seen CT make anything in this color recently.