Why are some skills in red and some in yellow

[Antmf]

When I hit cntrl T I see the skills that I can learn some are color coded in yellow while others are in a reddish color. What does that mean?

[trungdle]

It means that you do not have enough proficiency level to learn that skill, hence it's red.
To improve prof. Level, fill the bar up and press the plus button next to it.