Ghostly Flame

If the source has more than one color but at least one is red or black, then the damage is colorless and all the other colors are forgotten.

It does not change the color of the source, so that things that trigger on a red spell doing damage will still trigger. The damage itself thinks it came from a colorless source, however.

The effect is continuous and applies whenever something looks at the damage. If this card leaves the battlefield, damage from red and black spells will appear as its normal color. In other words, the color was not removed from the damage, the color just could not be determined while this card is in effect.