Lovely image there, Tom.
Ok, I'm going to venture into territory that I'm not 100% sure about and I cannot find the science page I viewed it so help me out anyone who does know better than I appear to: as light drops and we increase the shutter speed, bearing in mind photons do not hit the sensor all at the same time, therefore colour accuracy will suffer the higher shutter speed increases.
From my understanding, photons hit the sensor in the same way rain falls, in an irregular pattern. So, increase the shutter speeds higher leads to less photons hitting sensor with relevent colour info. As we're dealing with reflected light from our subject the photons have to bounce off our subject to our sensor to give us the colour.
So, given that sensors become more efficient and give us clean high ISO's nature (light/photons) won't be changing. I hope I'm making myself clear here as I'm not that efficient at getting my point across!