Color is the first thing a buyer judges and the last thing most product teams specify. By the time somebody asks how the housing gets its shade of slate gray, the mold is cut. There are only three real answers — masterbatch at the press, pre-colored compound, or mold natural and paint — and they differ by an order of magnitude in cost, minimum order, and how reliably lot ten matches lot one.

Masterbatch: Color Added at the Machine

A masterbatch is a highly loaded pigment concentrate in a carrier resin, supplied as pellets and metered into the natural resin at the molding machine's throat, typically at a letdown ratio between 1 and 4 percent. The screw does the mixing.

It is the default for good reasons. The molder buys one natural resin and runs any color from it, so a color change is a purge rather than a new qualification. Minimums are small — 25 to 55 lb colors a lot of parts — and cost is modest, $0.08 to $0.35 per pound of finished part.

The tradeoff is dispersion. Because mixing happens in a screw designed to melt plastic rather than compound it, poorly dispersed pigment shows up as streaks, swirls, and variation near gates and weld lines, worst on thin walls and long flow paths. It is also process-sensitive: screw speed, back pressure, or regrind fraction all shift the shade. Some cosmetic complaints are color problems rather than geometric ones, a distinction worth keeping straight against the mechanisms in injection molding defects.

Pre-Colored Compound: Color Locked In Upstream

A compounder melts pigment into the base resin on a twin-screw extruder and pelletizes it, so every pellet arriving at the molder is already the finished color. Dispersion is excellent, shade consistency is far better, and process changes at the press cannot shift it.

This is what you use when color is a brand asset, when the part is large and highly visible, when the resin is difficult (glass-filled, flame-retardant, or a grade where pigment interacts with additives), or when a regulated product needs certified traceability.

The costs are real. Compounded color adds roughly $0.25 to $1.10 per pound, minimums start at 500 to 2,200 lb per color, and every extra color is another SKU you forecast, store, and eventually write off. Lead times run three to six weeks against masterbatch's one to two. For a family with six colorways at modest volume, compounding can tie up more working capital than the tooling did.

Painting: When the Color Cannot Come From the Resin

Spray painting gets you effects no pigment can: metallics with real flake orientation, piano gloss, soft-touch textures, gradients, and two-tone masking. It also hides surface flaws — a part with sink marks can look flawless under primer and topcoat.

It is by far the most expensive route. Budget $0.40 to $2.50 per part for a two-coat finish, plus $400 to $3,000 for spray fixtures per geometry, plus 3 to 8 percent yield loss from dust inclusions even in a good line. Paint also adds a failure mode: adhesion. Low surface energy resins such as polypropylene need flame or plasma treatment before primer holds, and qualification is a cross-hatch tape test to ASTM D3359 plus a chemical rub, not an eyeball. Soft-touch finishes carry a service-life question of their own, examined in soft-touch coating, and the parallel decision on metal follows powder coating versus wet paint.

Painting also complicates end-of-life: a painted part is much harder to recycle cleanly, which matters if you are building a story around recycled plastic.

Matching a Color and Making It Stick Across Lots

The most common mistake is handing a factory a Pantone number and assuming that settles it. A Pantone chip is ink printed on coated paper. Plastic scatters light differently, and the same formulation reads differently on a gloss surface than a textured one, in a 2 mm wall than a 4 mm wall. It is a starting point for the colorist, never the standard.

What you need is a physical color standard: a molded plaque in your resin, at your wall thickness, with your surface finish, signed by both parties and retained at each site. Then define acceptance numerically.

  • Specify a spectrophotometer color difference limit, commonly delta-E below 1.0 for Grade A surfaces and below 1.5 for secondary parts.
  • Name the illuminant and observer conditions, and require a second illuminant check to catch metamerism — samples that match under store lighting and diverge in daylight.
  • Require measurement on first article and at a stated frequency during the run, with data submitted.
  • Control regrind percentage explicitly. Regrind darkens and yellows color over successive passes, and an uncontrolled policy is the most common cause of lot-to-lot drift.
  • Approve parts that share a color as a set. ABS and polycarbonate at the same nominal color rarely match without separate formulations.

These decisions belong with material, texture, and finish selection inside the CMF design process, not with purchasing.

How Color Behaves Over the Product's Life

Pigments are chemistry, and chemistry ages. Three failure modes account for most complaints.

Ultraviolet fading

Organic pigments — most bright reds, oranges, and violets — fade fastest. Carbon black at 1 to 2 percent loading is effectively the best UV protection available in plastics. Any part living outdoors needs a UV absorber plus a hindered amine light stabilizer alongside the colorant, qualified with accelerated weathering rather than assumed, as covered in UV-resistant plastics.

Chemical attack and staining

Sunscreen, insect repellent, hand sanitizer, disinfectant wipes, and cooking oils all attack colored plastics and paint. White and light grays stain visibly; paint can craze or soften. Test with the actual chemicals, not a generic panel.

Interaction with the base resin

Pigments are not inert additives. Some nucleate crystallization in polypropylene and change shrinkage, so a colored part comes out dimensionally different from a natural one. Others reduce impact strength or invalidate a flammability rating. Always mold qualification parts in the production color — a constraint that belongs in the material decision described in how to choose the right plastic.

Get the Color Strategy Set Before Tooling

Wall thickness, texture, gate location, and colorway count all interact, and the cheapest time to resolve them is before steel is cut. Projects House sets color and finish strategy for US clients and runs the qualification with molders through a global manufacturing network. Send your part design and target palette through our contact form.