I've noticed different colored numbers appearing during combat. There appears to be green, red, blue, yellow, and white numbers. Green seems to clearly represent healing instead of damage.
What does red, blue, yellow, and white numbers represent?
As you have guessed, green numbers are healing.
Red numbers are standard damage.
Yellow numbers are the damage dealt when your character scores a critical hit.
White numbers I initially thought to be ability- or status-based damage, but after some more testing I believe it may be non-critical damage that ignores armour, such as statuses or abilities that specifically take a percentage of health, or Darth Sidious' Deathstroke ability (but only some of the time as it has a 25% chance to ignore armour).
Blue numbers are special damage (but not critical special damage, critical special damage is yellow). Special damage is dealt by attacks that specifically say they deal special damage, such as Talia's Harrowing Assault, or the Jedi Consular's Attack as Defense.
White Damage is unmitigated damage. This means it cannot be resisted/evaded and is unable to crit.
All White Damage attacks ignore armour by default. Some White attacks ignore armour/protection, but not all white attacks ignore protection, only armour.
Examples of effects/attacks that deal unmitigated damage: