Multi-colour 3D printing options: layer swaps, multi-material, paint, assemblies

There isn’t one way to print in multiple colours, and the most expensive way isn’t always the best. If the colour changes with height, like a name sign with raised letters, pausing to swap filament is enough. If two colours must sit side by side in the same layer, you need a multi-material system, and you pay for it in plastic purged on every colour change. This lesson compares five options and works out how much gets thrown away.

1. Swap filament at a layer (M600 or pause)

The slicer inserts an M600 command at the layer you pick. When the printer reaches it, it stops so you can unload the old filament, load the new one and carry on. In PrusaSlicer, drag the layer slider to the layer and click the orange + icon.

• Can do: colour that changes with height: a base in one colour and lettering in another, signs, keychains, terrain maps.
• Can’t do: two colours in the same layer.
• Limits: use the same material type for every colour, and it doesn’t work with sequential printing (one object finished at a time). Someone has to be at the printer when it reaches that layer.

If your firmware doesn’t support M600, use a pause instead (PrusaSlicer’s Insert pause print adds M601). The same pause is how you embed magnets or nuts mid-print. Make the pockets tight, or a magnet can jump onto the nozzle as it passes.

Design for it: give the colour boundary a clean horizontal edge, for example letters raised 1–2 mm on a flat base. Make the letter height a whole number of layers so the swap lands exactly on the edge.

2. Automatic filament switcher on one nozzle

A unit that feeds several spools into a single hotend and swaps between them mid-layer, so two colours can sit side by side, such as a pattern on the side of a model.

The price is purging on every change. The old colour left in the hotend has to be pushed out until the new colour runs clean, into a wipe tower (prime tower) or a waste blob. Prusa notes that the wipe tower’s size depends on the number of colour changes, not on the size of the objects.

3. Multiple toolheads (tool changer / IDEX)

Each colour gets its own nozzle, so there’s no need to flush old colour out of a shared one. Purging drops a lot (a little remains to keep flow steady), and you can mix materials, such as a PETG part with a support material that peels off easily. In exchange the machine is more complex, nozzle offsets need calibrating, and the number of colours is limited to the number of heads.

4. Paint after printing

Print in one colour and paint it. You get colour detail no printer can do, like gradients and fine patterns, with zero purge waste, but it costs hands-on time and days of drying. Steps are in Sanding, priming and painting prints.

5. Print separate parts and assemble

Split the model by colour, print each colour on its own, and assemble with pins, snap-fits or glue. Colour edges are as sharp as they get, nothing bleeds, any single-colour printer works, and each part can print in its best orientation. Joining methods are in Joining 3D prints.

The five side by side

Method	Colours in one layer	Waste	Needs you at the printer	Good for
Swap at layer	no	very little	yes, at every swap	signs, logos, raised text
Single-nozzle switcher	yes	high, scales with changes	no	surface patterns, hands-off multi-colour
Multiple toolheads	yes	low	no	multi-colour, multi-material, soluble or easy-peel supports
Paint	yes	none	hours of handwork	display pieces, fine detail
Separate parts	yes (per part)	none	you assemble	crisp colours, big parts, toys

Working out the purge waste

Example: a two-colour keychain, 20 mm tall at 0.2 mm layers = 100 layers, both colours on every layer. The part itself weighs about 20 g.

The slicer starts each new layer with whatever colour is already loaded, so there’s roughly 1 change per layer = 100 changes. Say your slicer’s purging volumes table shows 300 mm³ per change (real values vary by colour pair and machine; look them up in your own slicer).

1. Total purge = 100 × 300 = 30,000 mm³ = 30 cm³
2. Weight in PLA (density about 1.24 g/cm³) = 30 × 1.24 ≈ 37 g, almost twice the part
3. As 1.75 mm filament (cross-section π × 0.875² ≈ 2.405 mm²) = 30,000 ÷ 2.405 ≈ 12.5 m

Put 4 keychains on the plate and each layer still needs just one change (all objects get the first colour before the swap). Purge stays at 37 g, but split four ways it’s about 9 g per keychain.

Compare a redesign as a layer swap: base in one colour for 90 layers, letters in the other colour for the top 10. That’s one change, wasting only the filament pushed out during the swap.

Before you print in multiple colours, compare the slicer’s purge figure with the weight of the part. If the purge is bigger, redesign, or fill the plate with copies.

Cutting waste on a multi-material system

• Wipe into this object’s infill. Uses the part’s infill as the dump. Saves a lot, but dark purge can show through light walls; more perimeters help.
• Wipe into this object. Mixes colours on that object’s surface. Fine for mechanical parts where colour doesn’t matter.
• No sparse layers in PrusaSlicer (still experimental) skips wipe tower layers that have no tool change. In Prusa’s test set it cut filament on the tower by about 16%. Crash detection must be turned off.
• Lower purge volumes step by step, and test the hardest pair (dark to light).
• High-flow nozzles need more purge. Prusa says that with a CHT-style nozzle the wipe tower grows by more than half.

Common mistakes

• Mixing materials at a layer swap, such as PLA and PETG. Layers don’t bond, or the nozzle clogs.
• Too little purge going black to white. The white comes out grey or pink.
• Wiping into infill behind thin walls. A shadow of the dark colour shows through.
• Tall, thin wipe tower. It topples mid-print. Use the slicer’s stabilization cone.
• Resuming right after loading. Users report oozing or a gap where printing restarts. Purge until the new colour runs clean and pull off the blob before you resume.
• Using a multi-material unit for a height-only colour change. Tens of grams wasted for nothing.

Next: Outdoor and food-contact prints

Sources

• Color change — Prusa Knowledge Base
• Insert pause or custom G-code at layer — Prusa Knowledge Base
• Smart wipe tower — Prusa Knowledge Base
• MMU3: Prusa nozzle vs CHT nozzle — Prusa Knowledge Base