Why don't my horses turn unicorns on minecraft when i use the poition?

In minecraft, horses can only be transformed into unicorns if they are actually a special type called a "skeleton horse" or "zombie horse." Regular horses cannot be turned into unicorns using potions. Instead, unicorns are typically represented by horses with a specific name or texture pack in various mods or custom servers. Make sure you are using the correct version or mod that allows for unicorns, as they are not part of the standard game mechanics.