That is some good information. Here in the desert just walking my dogs on the summer mornings, clothing color makes a big difference. If I wear a dark shirt, I can usually feel the sun heating up my shirt and feel hot most of the walk. That it could make such a difference in a northern winter is very surprising and interesting to me.

It seems these additives in detergent generally reduce UV and increase blue light according to Wikepedia: "Optical brighteners, optical brightening agents (OBAs), fluorescent brightening agents (FBAs) or fluorescent whitening agents (FWAs) are dyes that absorb light in the ultraviolet and violet region (usually 340-370nm) of the electromagnetic spectrum, and re-emit light in the blue region (typically 420-470nm).... These additives are often used to enhance the appearance of color of fabric and paper, causing a perceived "whitening" effect, making materials look less yellow by increasing the overall amount of blue light reflected."