Originally Posted by
Toxcatl
XP from a drill goes to all its skills equally, if they are all key skills. For example, Hurdle Jumps is a Hard drill (4 XP) and trains 3 skills (Bravery, Aggression and Speed) for 4 / 3 = 1.33 XP each on level 1, if all these skills are white.
If there are grey skills, they receive 25% less experience from training, and this XP goes as bonus to the white skills of this drill equally. So a drill with grey skills trains its white skills faster, but for the cost of XP spent on grey skills. Total quality gain of the player is unaffected: drills of the same level improve player's quality with the same rate regardless of having or not having grey skills.