Essa é conhecida, no help fala sobre isso inclusive na parte do daylight. Resumindo, vc tem que desmarcar a opção "Screen (Soft) Compositing Of Layers" (é isso que deixa preto com o daylight) e ligar o "Scatter Indirect Illumination" pra pegar a luz do céu, como mostra no help:
[quote:376b3feda6][i:376b3feda6]Using Sun & Sky with SSS Materials
To use a mental ray fast SSS material together with the high-dynamic range Sun & Sky solution, be sure to turn on Scatter Indirect Illumination on the material's Advanced Options rollout so that the material can scatter the skylight, which is considered indirect.
Also, turn off Screen (Soft) Compositing Of Layers, also on the Advanced Options rollout; otherwise the output of the SSS shaders is clamped to a low dynamic range and will appear to render black.[/i:376b3feda6][/quote:376b3feda6]