If I can give an answer with reference to 5 Buddha mandala as I think it draws together the iconography into a satisfying whole.
As it's name suggests the 5 Buddha mandala 5 Buddhas at each compass point with one at the center. Each Buddha displays their own mudra. Each mudra points to a quality of that Buddha and thus to a quality of the enlightenment experience.
1. Aksobhya The blue Buddha
Mudra is the bhūmisparśa or earth touching mudra. The hand touches the earth. This points to the imperturbable.
2. Ratnasambhava - the yellow Buhha
Mudra is the dana or giving mudra. The hand points downward and out (shown by NeilD). This points to generosity.
3. Amitabha - the red budda
Mudra is the meditation or dhyana mudra. Hands together (show by NeilD). This obviously points to contemplation
4. Amoghasiddhi - the green buddha
Mudra is the fearlessness or abhaya mudra. Hand is up and poitn forward (shown by NeilD). This is self explanatory I think.
5. Vairocana - the white buddha
Mudra is the wheel-turning or Dharmacakrapravartana mudra (again shown by NeilD). This which fits his central place in the mandala, bringing all the other qualities together.