Например, так:
class BookAdmin(admin.ModelAdmin):
list_display = ("pk", "get_title_or_nothing")
def get_form(self, request, obj=None, **kwargs):
if obj.type == "1":
self.exclude = ("title", )
form = super(BookAdmin, self).get_form(request, obj, **kwargs)
return form
ну, или с Вашей предметной областью:
class CarAdmin(admin.ModelAdmin):
list_display = ("pk", "model", "vin")
def get_form(self, request, obj=None, **kwargs):
if 'Red' not in obj.color:
self.exclude = ("field1", "field2")
form = super(CarAdmin, self).get_form(request, obj, **kwargs)
return form