From China Digital Space
APEC蓝 (APEC lán): APEC blue
The color of the skies over Beijing during the Asia Pacific Economic Cooperation (APEC) summit in November 2014.
In an effort to cut air pollution by 40% for the summit, the city gave students and workers a bonus "Golden Week" holiday, halted factory and construction work, enacted alternate driving days for even and odd license plates, and even put a temporary stop to barbecues and cremations. The skies were indeed bluer, but the extent of the improvement was tough to measure—air quality data from the U.S. embassy, available to denizens on the China Air Quality Index app and considered more reliable than municipal reports, was censored. "APEC blue" thus describes a hue reserved for foreign dignitaries that cannot be quantified.
Songyingjie (@宋英杰): It's said that Beijing only had two cases of smog this year: once before APEC, and once after. (November 19, 2014)
Caijingnüjizhebuluo (@财经女记者部落): #APECblue tells us: It's not that the government can't do it, it's that you aren't important! (November 6, 2014)
'''#APEC蓝#''' 告诉我们：不是政府做不到，是你们不重要！ [Chinese]
See also Chai Jing blue.