All the answers are right, but I want to point out that You should use an advanced team.
It "seems" to be difficult, but it is not.
Once You changed some colors You will want to change the order of some elements, add details or extra features and so on. For many things You find instructions on the matching questions here.
The functions in the qa-theme.php are a little bit doucmented and mostly easy to understand, the css file has the most logic structure I have seen so far.
I recommend that You start with an advanced theme where You include all the functions, see instructions on the advanced theme section. So You can play around without thinking which functions You need to include.
And yes, on the first view one thinks ohh, this is complicated. But it is pure php, no smarty, no template files, nothing extra. You as well could describe it as "elegant"(if this is the matching phrase in english.)
And whenever You need help on a special issue, the community here is excellent as well.
I was looking a long time for a good q&a solution, here it is, really, I dont see any other script with so many advantages.
And, as mentioned by DisgruntledGoat, firebug is a must for any developer, makes developing 75% faster.