Why there are shades differences in garment dyeing?

Fabrics have color shade before wash. It’s invisible before wash.
If fabric shades are mixed in one washing batch, it’s impossible to avoid shade issues.
During the dyeing process in the machine, the force and fraction occur randomly. It creates slight different shade within one batch.
The fabric condition before wash decides the color shade & garment dye quality after wash. Especially, some silicone softeners do not remove during the garment-dyeing process. It will cause uneven dyestuffs absorption.

Why I can not match the color to the standard?