我在文档中找到了答案:

I found the answer in the documentation:

forms.py 中的额外类不是必需的

The extra class in forms.py was not necessary

#form.py
from django.forms import ModelForm
from django.forms.widgets import TextInput
from .models import Category

class CategoryForm(ModelForm):
    class Meta:
        model = Category
        fields = '__all__'
        widgets = {
            'color': TextInput(attrs={'type': 'color'}),
        }

在管理员中:

#admin.py
...
from .forms import CategoryForm

...
class CategoryAdmin(admin.ModelAdmin):
    form = CategoryForm
    filter_horizontal = ('questions',)
    fieldsets = (
        (None, {
            'fields': (('name', 'letter'), 'questions', 'color')
            }),
        )