Patagonia used to make white capilene base layers - not sure if they still do but they certainly have light grey www.patagonia.com - great for glaciers in the heat of the day when darker colours tend to absorb more heat. Capilene wicks very nicely as well.
That's interesting Jon, I did not think that darker coloured base layers would make much difference to heat absorption, since I thought that only outer layers "reflected" the heat back and that if so, then the heat dissipated and would not penetrate through subsequent layers???
They won't make any difference when worn under other layers, but when it's really warm - and glaciers at altitude get very, very warm - and you're just wearing, say, a baselayer top and trousers, the colour does make a difference.
Patagucci do indeed do a light coloured base layer, saw one in Outside in Hathersage today. I was tempted to buy it but didn't know much about the Capilene fabric, until Jon's post above.
One advantage I find of lighter coloured base layers is that they seem less likely to attract those damn Scottish midges.
Capilene works really well. It was pretty much the benchmark baselayer until Dryflo and Powerdry appeared and is as good or better than either for wicking in my experience. The only disadvantage is that the fabric uses a treatment rather than the physical structure of the fabric, so wicking performance deterorates, albeit very gradually, with sustained use and washing.
