UNITY_LIGHTMODEL_AMBIENT not working in Unity 2018 LW RP?

I’ve created a surface shader from Create > Shader > Standard Surface Shader and added the tags “RenderPipeline” = “LightweightPipeline” “LIGHTMODE” = “LightweightForward” and then the shader is working, that is it does not render pink anymore. But if I use the UNITY_LIGHTMODEL_AMBIENT.rgb or .xyz I only get a light grey colour, no matter what colour I set the Environment lighting in the Lighting Window, and it does not matter if I set it to gradient or colour and set all sort of crazy colours, all I get in the shader is a light grey.
It works if I create a project using the old “3D” template, so what’s the difference here? How do I get the Ambient lighting colour in the LW RP?

you can get the color with unity_AmbientGround, unity_AmbientSky or unity_AmbientEquator