A color shift after milling means the shade changes from premix to finished grind. It usually signals that pigment was not fully dispersed, or that milling changed particle size, flocculation, or vehicle. Because color strength and hue depend on dispersed particle size, an incomplete or over-aggressive mill pass moves the shade. The mechanism starts in pigment dispersion fundamentals.
Often under-dispersion in premix - the pigment was never fully wetted, so strength appears only after a proper mill pass or, if over-milled, jumps the other way.
Can milling change the hue?
Yes. Particle size shifts light scattering; over-milling can intensify or dull a shade depending on the pigment.
What causes graying?
Metal contamination from worn steel parts or wrong media. Use zirconia media and check the separator and chamber.
Why does color shift on letdown?
Flocculation can return when the vehicle or solvent balance changes; stabilize the letdown and keep dispersion stable.
How do I prevent shift?
Fix premix, hold media/size/time/temperature constant, avoid contamination, and verify with a drawdown at the same fineness each run.
Is heat the culprit?
Heat changes viscosity and can soften the vehicle, indirectly moving gloss and shade; control temperature during the mill pass.
