With this, I get a full A4 page with the shading colors. This worked until the beta 2018-06-22 16:02 and the desired output is shown when using live.contextgarden.net.

Even in the previous mtx-context | current version: 2018.06.22 15:55 I get a full A4 page with the shading colors if I use Luatex 1.09.0 Development id: 6823 The desired output is obtained if I use Luatex 1.08.0 Development id: 6731 So I think the latest experimental binary is problematic in this example. Best, Akira