RandomBackgroundActor_BP does not randomize

[drostifrosti]

I would like to have the texture for a material randomly selected from a directory, which does not randomize the selection. Eventually I realized that it is not even possible to randomize a simple color. I followed the steps on page 30 of the NDDS documentation for randomizing the color:

1. clean checkout via git lfs clone and rebuild for UE 4.22.3
2. in the TestCapturer level, select the RandomBackgroundActor_BP and choose M_NVBasic for Element 0
3. double-click M_NVBasic and rename color block to "BaseColor"
4. in RandomMaterialParam_Color, check "Should randomize", rename element 0 of Material Parameters Names to "BaseColor", remove the other 2 names
5. click on Play

I expected the color of the sky to show a random color for each generated frame, but it just stays black.
Can someone please explain what further steps are missing or wrong?