photism

from Wiktionary, Creative Commons Attribution/Share-Alike License

• n. A luminous appearance, image or subjective perception of a hallucinatory nature.
• n. The color that a synesthete may report seeing in association with a particular letter or number

from the GNU version of the Collaborative International Dictionary of English

• n. A luminous image or appearance of a hallucinatory character.

from The Century Dictionary and Cyclopedia

• n. In psychology, a reproduced sensation of color regularly accompanying the arousal of sensation in certain other sense departments, especially in that of hearing: the commonest form of synæsthesia.