Dear Xuejiao Lin,
Regarding item d).
Most of upper-air Chinese stations are displayed in orange in WDQMS web tool due to the fact that humidity is missing above 100hPa in China's upper-air reports. On the other hand, the surface observations are shown in orange due to the fact that the reporting frequency is below the target (between 30 and 80%). That is the case for most of Chinese stations using the GBON baseline, where the target is 6 and 24 observations for 6-hourly and daily views, respectively.
Regards,
Cristina