Here is something I didn't actaully spot while watching but noticed in promo pictures , now when I watch Enterprise I look for it. Both Tripp and Archer had the top of their hair dyed a blond colour. In the show , it just looks like the lights from overhead are shining on their hair, but in other media ( promo pics, interviews ) it was quite noticable. You can see it in show sometimes when you get a side shot of their heads, the top half is lighter then the bottom half.
I'm not even sure if it was dyed for the show, Reed didn't seem to have the same thing done and his hair is quite dark too. It may very well have been a personal style chioce by the acters and had nothing to do with the lighting on the show. I guess it only really stood out because it very obvious in photos but not at all in film,
Cheers,
Kytee