Pardon the necro, but I'm looking to see if anyone else has come across any methods to achieve what the OP asked for.
I came across the global strings for 'immune' alerts and such as was able to remove them completely as well as alter their text:
Code:
COMBAT_TEXT_DEFLECT = "Deflect"
COMBAT_TEXT_REFLECT = "Reflect"
COMBAT_TEXT_IMMUNE = "Immune"
COMBAT_TEXT_RESIST = "Resist"
COMBAT_TEXT_ABSORB = "Absorb"
COMBAT_TEXT_BLOCK = "Block"
COMBAT_TEXT_DODGE = "Dodge"
COMBAT_TEXT_PARRY = "parry"
COMBAT_TEXT_EVADE = "Evade"
COMBAT_TEXT_MISS = "Miss"
These strings are found in Interface\FrameXML\GlobalStrings.lua in enUS.mpq.
You can, for example, change COMBAT_TEXT_IMMUNE to "LOL IMMUNE!@#" or a completely blank string "".
Right now I'm looking to find the ones for other peoples effects, like "Snared (Bobthefrostmage - Bobthefrostmagesserver)".
Blanking out white hits I would bet is doable as well, I would think it has a string for its own color.