Several colours on one part

A part has one main material. Some of its faces can wear other materials, each on a selection of faces: a red body with a blue top, a grey housing with a painted logo. It is still one part: it is selected, moved, merged and exported as one, and it stays closed, because the faces in another colour share their edges with the rest.

Parts like this also come in from other programs. A Blender object with several materials opens as one part with its colours, from GLB, glTF, FBX and OBJ. A STEP body whose faces are painted in more than one colour (SolidWorks and Creo do that) opens as one closed part with each colour on its faces.

Colour some faces

1. Select the part and press Enter for Edit mesh, then 3 for polygons.
2. Pick the faces: click, box or brush. A double-click picks a loop.
3. Press Colour in the Edit mesh bar, or hold C over the view. The colour wheel opens, and only the picked faces change as you move. Click to keep the colour.

Or drop a material from the materials dock onto the picked faces, or press its Assign: with faces picked in Edit mesh, the material goes on those faces and not on the whole part. Each of these is one step in the undo list.

See and change the colours of a part

With one part selected, Properties shows its colours as cards in the material strip: the main one first, then each colour on some faces. Point at a card to see how many triangles wear it.

Right-click a card

Pick these faces picks those faces in Edit mesh, to see them, change them or colour them again. Recolour these faces… gives them another colour.

Give these faces back

The same menu has Give these faces back to the main colour, and a face colour card has a small arrow button that does the same.

The main colour

Its menu reads Pick the faces in the main colour and Recolour the main colour…; it has nothing to give back.

A material given to the whole part, from the dock or the colour wheel with no faces picked, becomes its main material. The faces in other colours keep theirs.

What keeps the colours

• Undo and redo, saving the scene and opening it again, and the recovery copy.
• Merge, Split, Decimate and the mesh tools that keep the triangles they do not change. A tool that builds a new surface (a remesh, a boolean) gives the part its main colour all over.
• Select by colour finds a part by any of its colours. Merge by colour goes by the main colour.
• Export: GLB and glTF write a primitive a colour, OBJ a usemtl for each, FBX a material for each polygon, USDZ a subset of faces a material. Blender reads each part as one object with its materials. PLY writes the colours on the points. STL has no colours.