In general they seem to go for 'beauty lighting' on this show. The natural light, but not harsh natural light (yay overcast London) and then the soft, rather shadowy, but not dark lighting of the interiors, which plays very nicely with sculpted jaws and cheekbones. I'm thinking about how many of the 'late night doing paperwork' scenes are done with low lights, rather than the bright overhead florescents that would have been equally valid as nighttime office lighting.
Also, Matt Devlin is a confident character. He holds himself like someone who has power. Though he has vulnerabilities (and we adore that about him) in general, this is a strong man. He's not given to maudlin introspection, or self-doubt, he's just not self-reflective in that way. And as much as I adore the emo, and have the fondest of fond places in my heart for Archie and Lee, there is also something quite attractive about unadulterated confidence, even cockiness. While I personally would love Mattie to get a bit more tortured for maximum hawt, anyone who likes their men less twisted is bound to find Matt Devlin as he is now more attractive than previous, more complicated and damaged characters of Jamie's.