As seen in the figure 1 below, white light falls along the Planckian Locus (or black body locus) on the Chromaticity Diagram. This means that depending on where the white light falls along the black body locus, the light can be bluer or yellower than another white light. Also depending on whether the light falls above or below the black body locus, it can be slightly green or slightly pink, respectively. 
 
White LEDs are sorted in a process called binning. Binning ensures consistency of color and quality of light. First, LEDs are sorted by the amount of light they produce (Lumens or Luminous Flux). Next, they are sorted by the color temperature of the white light they produce (CCT – Correlated Color Temperature). Finally, they are sorted by the voltage drop across the LED as measured at 25° C (VF – Forward Voltage). 

ANSI C78.377A establishes a minimum requirement for Energy Star certification (see figure 2). This specifies a bin size approximately correlated with the color variations we currently experience with commercial compact fluorescent lamps today. This is a 7-step MacAdam ellipse. This means that the color difference from one LED to another, defined by ANSI could be as much as 350K difference. This is a noticeable difference in color temperature. While this is what is required for ES certification, respectable manufactures of white LED product have narrowed their binning selection to a 3-step MacAdam ellipse.  

Solais has taken this a step further . . . literally. Solais requires a 2-step MacAdam ellipse binning for LEDs. This means that the potential color difference between LEDs in the same bin will be less than 120K, which could be noticeable at the LED itself, but not on the surface being illuminated by the LED.