The ‘Transparent BSDF’ shader node does not reflect (as in diffuse reflection) any light, meaning that it always renders as a black surface regardless of the value provided in the color parameter, all that parameter does is control the alpha/transparency of the surface, not it’s color (as the name would imply).
I modified a local version to fix that behavior by adding a new input to the node (called ‘Alpha’, like the principled bsdf node) that now controls the transparency of the surface, and ‘Color’ now is the color of the surface.
This is the main change, the rest is just boilerplate stuff to support the new parameter.
result.radiance = color.rgb * alpha; // previously: vec3(0.0); result.transmittance = vec3(1.0 - alpha); // prev: abs(color.rgb);
This would be my first contribution to blender so I’m not too sure how you prefer I set this up. Is there something I should know before I create a ‘patch’ for this ? Should I create a new type of node since this could be thought of as a breaking change ? Would you prefer I leave this to another maintainer ?