Cthulhu Insanity Dice comes with two different dice. One has green tentacles and is used for immediate effects when a character is traumatized and suffers a temporary insanity (the Temporary Insanity die). The other has red tentacles and is used for longer term phobias (the Phobias die).
In the 6th and 7th editions of Call of Cthulhu, an investigator suffers a temporary insanity when they have suffered 5 or more sanity points at one time and passes their idea test. Afterwards, a mild phobia is applied to the investigator. For other game systems, apply an insanity or phobia when the rules apply some mental trauma or when a character loses control of their actions, such as failing a fear test. The duration of the insanity should be proportional to the horror the character is facing; the more terrifying, the longer it should last.
(taken directly from dice literature)