LEDs, like many semiconductor products, are "binned" or sorted into varying groups based on performance characteristics due to "natural" variations in the manufacturing process.
Typically, LEDs are binned based on color/tint, Vf, and flux (brightness). Generally speaking, higher flux and lower Vf are desirable attributes (more light, less power = greater efficiency) - but due to the uncontrollable variations in manufacturing (as well as trying to maximize yield), there are only so many of these.
Here's my
terse guide to Luxeon bin codes.
White LEDs have a tendency towards blue tints because they're really a blue LED coated with a yellow phosphor. Oftentimes manufactuters skimp on the phosphor or don't use very good phosphor, so the blue tint is strongly visible.