They look like normal Krabby Patties, but are different colored.
The Pretty Patties come in 22 known colors:
A dark shade of brown
A dull blue-gray
Yellow with Green Spots
Green glow in the Dark
Rainbow (all the colors in up and down stripes)
Green with black and purple stripes
Role in series
They are created by SpongeBob and are basically Krabby Patties, but in assorted colors. They were loved by all of Bikini Bottomites until the colored patties turned their skin into an assortment of colors, and even caused three citizen's' tongues to different colors, one glow in the dark, one yellow, and one orange with green dots. Everyone hated them afterward, and they haven't been seen or sold since.
The venue in which Pretty Patties were sold was a stand created by SpongeBob and Patrick. There was a stand to sell the patties, and right next to it was a stand that gave money away to customers. The stand was colored yellow, blue and was later taken over by Mr. Krabs, and the Krusty Krab key was given to SpongeBob. After the episode, the stand no longer existed.
The last Pretty Patties customer was the man with the glow-in-the-dark tongue.
SpongeBob might have been hinting that he painted the Pretty Patties with edible paint, because when he first introduced them, the patties were displayed on a paint palette.
If Pretty Patties utilized the same recipe for Krabby Patties, SpongeBob would owe Mr. Krabs royalties.
When SpongeBob revealed the Pretty Patties to Squidward and Mr. Krabs, he says, "Available in 6 designer colors." However, they are seen in approximately 22 different colors. It is possible that he added the colors as they got more popular.