Once calibrated the Color gamut on the 11" is very good. I calibrated all my monitors so they look the same, including my Cintiq 21ux and older ACD 24".
The MacBook air screen on my 11" is Samsung. The 13" screen is more prone to Color shift if your not viewing it from it's sweet spot and you can visibly see the Color change tint if you adjust the tilt. It may not be much of a change, but it's enough of one of your working on a color sensative project, the 11" seems to suffers less due to the narrower screen and higher pixel density.