You could check out 'Blossoming Hearts'. In this manhwa, there's an LGBT character with pink hair. The art style is unique, and the story is full of emotions and surprises.
There's 'Love is an Illusion' which has a character like that. It's quite popular among the LGBT community.
There are several. 'My Secret Romance' has a character like that. It's a popular one.
There are several like 'My Pink-Haired Heroine' which has gained a lot of popularity. The lead's pink hair adds to her charm and the story's appeal.
Often, characters with pink hair in manhwa are associated with a certain charm or quirkiness. It could be used to represent a rebellious nature or a non-conformist attitude. Also, it might be just a visually appealing trait to make the character more memorable.
The cartoon might showcase the contrast in their personalities. Maybe the pink-haired girl is more lively and the blue-haired one is calmer.
I'd recommend 'Pink Blossom Dream'. The main female character has charming pink hair and the story is full of romance and fantasy. It's a great read!
Another one could be 'Sailor Moon'. Some of the Sailor Scouts have pink hair. For example, Chibiusa has pink hair and is a beloved character.
There are a few like 'Fairy Tail' where some fairy characters have pink hair. But it's not super common in old cartoons.
There's 'My Little Pony: Friendship is Magic', where one of the characters has pink hair. It's a popular kid cartoon.
One popular manga is 'Sailor Moon', where the main character Usagi has pink hair and is loved by many.