What do the different types of projectiles do?

There are three types of projectiles in the game: 

Armor-piercing (AP) shells are always marked blue. They are effective for firing at the side and rear of heavy and light vehicles. 

Shaped Charges (SC) are always marked red. These work well when hitting heavy or light vehicles that do not have specialized protection systems head on. 

High Explosives (HE) are always marked yellow. These deal damage even when they don't penetrate armor. If a HE projectile manages to penetrate the enemy's armor, it will cause a cause an internal explosion, completely destroying the inside of the enemy tank.