A Ryze Question

Certain mage spells are coded as 'crits' when they have empowered damage.

So when Ryze's Q hits an enemy marked by E, the Q damage is empowered and the numbers show up as purple.

Another example is Anivia; when she uses E on a fully 'chilled' target she either stunned with her Q or hit with a fully formed ult, the numbers show up as purple.

Yes it's the same principle. Its just an amplified damage. (Any number that is bold is doing more damage than the game thinks you should be doing at that point.) The little almost flame symbol that pops up next to the number is a critical damage indicator.