I cant find anywhere how I should connect inputs to Float3ToFloat (or any other similar) ShaderFx node. It works if I use ComputeFloat or Float3ToFloat with hardcoded values:
Could it be that you have shaders with the same name somewhere in the vvvv.exe scope? Shader names are global, you can’t have two shaders with the same name twice per vvvv instance.
Also if you change shader types, restart vvvv, sometimes older instances might be cached.
You are right, this seems to be a bug. You can get it to work if you add the stage keyword:
stage float4 Color = float4(1, 1, 1, 1);
But then you can only have one per shader graph. So if you use the same ShaderFX node multiple times in the same shader graph, the last node that gets evaluated will set the value for all. So for basic cases, the stage keyword helps, otherwise you have to make a new copy of the shader with another name until it gets fixed.