[Answer]-Django Inlining shows additional fields in the add dialog

InlineModelAdmin extra‘s default value is 3, so you can simply change it extra = 0 in PenInline declaration:

class PenInline(admin.TabularInline):                                               
    model = Pen
    extra = 0

https://docs.djangoproject.com/en/dev/ref/contrib/admin/#django.contrib.admin.InlineModelAdmin.extra

Or look at https://stackoverflow.com/a/2228821/3033586

Or remove ColorAdmin declaration and change last line to admin.site.register(Color)