Ever used a rocket hammer charge against a weak enemy? The damage numbers aren't yellow like they're supposed to be.
If I recall correctly, this happened in a patch shortly after lost souls got introduced to avoid lost souls making huge damage numbers all the time. I went into Tier 3 Guild Training Hall to find out what the limit was. We found out this:
468 damage shows yellow numbers.
473 damage shows white.
Since T3 bags have 61 defence, the limit for yellow numbers become somewhere around the defence being 11.5% of the total damage inflicted.