The basic criterion is that the minimum shifts in colours is larger than 0.03.
However, there are other cases:
 1. the minimum colour shifts <0.03 but the fitting of colour shifts w.r.t.
     the ELAIS fields is not reliable.
 2. the minimum colour shifts <0.03 but this minimum colour shift is either
     U-g or i-z, for which the fitting of colour shifts is less reliable than
    g-r vs. r-i, and the fitting appears to be not very reliable.