Training: White and grey area's. How does it work?

[Jackguiver]

I am struggling to find an answer on here about the relevance or indeed the benefit of focusing on key attributes in training.

Can anyone tell me:
Do grey skill percentages factor into overall ability %?
If not then surely fewer key attributes would be easier to train and develop, no?

However, I have literally just purchased an MC with 15 white (key) attributes and during training sessions with the team, he picks up lots of percentage points, regardless of the training schedule.

I'm a little confused with the new training system and have read all the posted tutorials (thanks people) but none of them really get into the detail I'm looking for.

If anyone has any ideas/tips/info I would really appreciate it.

Jack