Render Engine set to Cycles.
For Meshes their diffuse colour is shown in 3d viewport when the Viewport Shading mode is set to Material. Curves do not do this, is there any way to turn this on for Curve objects too? For example below, the silver-grey tubes are Curves and I'd expect them to show the diffuse of the materials assigned to them (black, orange, and blue).
Viewport Shading: Materials
Renders like this, this is OK, and so is live Viewport rendering:
The problem is Curves aren't showing their colour, instead a default grey. It doesn't matter which cycles shader-type is used.