While writing the bug report on Haste, I had an idea that seems reasonable to implement.
In this screenshot, the player is under the effect of Haste (supposedly).
The color of mana being generated is already communicated to the player via outline surrounding the numbers (in this case purple for Dark mana).
Is it possible to color code the number itself to reflect modification of normal mana generation, similar to the following proposed scheme?
Green: Bonus mana was generated because of Haste or similar positive status effect.
White: Unmodified natural mana generation amount.
Red: Reduced amount of mana generation because of Freeze or similar negative status effect.
In this way, the color of the number reflect any modifiers on mana generation while the outline still communicates what color mana was generated to the player.