The Chromatic Ghosts of Thomas

Thus it continued, a new yellow cat ghost materializing on the sixth night, only to mingle with a new red one on the seventh night, making a lovely orange-colored one; while on the eighth night a most peculiar cat ghost appeared that was what might be called a tortoise-shell cat ghost of all hues. We went to our room on the ninth night with considerable anxiety, not knowing what the last ghost of Thomas would be like; but we found that all the ghosts had combined to form one single ghost of spotless purity -- a white iridescent ghost with a white iridescent grin that faded away into the air and disappeared entirely.

Perhaps truth is stranger than fiction. Perhaps you may consider this blending of the ghosts stranger than the congregating of nine prismatic cat ghosts would have been. I can only say it is more logical.