> Traditionally rendering has been concerned with the RGB colors
I do need to point out that many (most?) so called physically based renderers are still RGB based, with all the downsides that come with that. Mitsuba is notable for also having spectral rendering, which is a distinct feature that models light as a spectrum instead of rgb triplet.
Man they really need to explain what is unique about it on the home page better. I know what differentiable rendering and spectral rendering are but neither are mentioned. I have no idea what a retargetable renderer is and it seems like nobody else uses that term at all (seriously - Google "retargetable renderer").
I do need to point out that many (most?) so called physically based renderers are still RGB based, with all the downsides that come with that. Mitsuba is notable for also having spectral rendering, which is a distinct feature that models light as a spectrum instead of rgb triplet.