Blancmange is a food that only appears in the episode "Squid's Visit."
It is a hot pink jello type of dessert with light pink frosting and there is also a cherry on the top of it. The color varies between the jelly body to the creamy top, the bottom being a darker pink while the top is a slightly lighter pink.
Role in episode
SpongeBob offers a plate of blacmange to Squidward after suggesting many desserts to make him comfortable and welcoming to his house, but the latter refuses to eat it. The reason Squidward denies this treat is because his vacuum cleaner is at stake.
Blancmange in real life is normally white.
Squidward says he doesn't know what it is. If SpongeBob copied Squidward's house, then that means Squidward had it in his fridge, meaning it's impossible that he wouldn't know what it is.