Opening the vents up will bring your temps up, as long as you still have sufficient fuel to burn. It looks like you're getting some good bark on there. It doesn't always have to be super dark. Because your temps are so low, the sugars in your rub probably just aren't turning as dark as what you see in a lot of pics.
Picking up on the temperature discussion, I've experimented with hot & fast cooks quite a bit over the last few months. Life is busy with kids, work, etc, so I'm always open to a time saver. I did a fundraiser a while back where I cooked 7 butts in my 22.5 WSM and did them 325-350. They got done MUCH quicker and turned out phenomenal. Good smoke ring, good smoke flavor, just as moist and juicy as ever. In other words, no one could tell the difference between those butts and the ones I've cooked at 275. Something to think about in the future and possibly give a try.
Eddie G. - Smoke Bomb BBQ coming off a Lang 48 Hybrid Deluxe