Unusual characters highlighted after calling colorscheme command

I encountered strange team behavior :colorscheme

.

I have some unusual characters by haskell-hide script like ∷

and →

. I don't have an option colorscheme

in mine .vimrc

, so these characters are displayed in the usual way:

After calling the command, :colorscheme default

these symbols are highlighted:

it will be great to understand what happens after calling this command and what exactly affects this behavior.

UPD

• Can you place some text here on a non-image form so we can try to reproduce it?

client ∷ Nick → Handle → IO ()

• What is the name of the file being edited?

*.hs

• ... output :set filetype
  
  

filetype=haskell