How to ensure color uniformity in plastic injection?

I strongly recommend you to perform color stability tests on representative samples from each production batch. This will allow you to quickly detect any color deviation from the RAL 5012 reference and take the necessary corrective measures.

The choice of material based on its characteristics is crucial, as not all react the same way to dyes. But the best solution is always to send a sample of the desired color to the supplier, at least for the first batch. And ideally, to keep the same supplier throughout production to ensure the uniformity of the parts and their color. I also invite you to read this article on the subject https://xometry.pro/fr/articles/moulage-injection-couleur/

Colorimetry is defined by a Delta E spectrum (combination of Delta L, A, B)… that is, acceptable deviations on the scales of primary colors and light.

Once the acceptable tolerance has been defined with the supplier, it is appropriate to ask for a colorimetry control for each production batch.

If production volumes allow it, a mass-dyed material is recommended to ensure a lasting tint. For lower volumes, a coloring at the base of the machine is preferred. The supplier must be equipped with dosers (weight or volume), to ensure the repeatability of the process. Beware, some materials are more difficult to dye than others! (ASA for example).

in ABS, no problem.

The material is not preferred based on its color, but based on the specification of the finished product…