Django Creating constraints on serializers - django

Question

I'm trying to extend Django's Poll app. Each poll will have 2 choices and either an image for each choice or a color for each choice, but not both. My models look like this:
class Question(models.Model):
question = models.CharField()
created_at = models.DateTimeField(auto_now_add=True)
class Choice(models.Model):
question = models.ForeignKey(Question, on_delete=models.CASCADE)
choice = models.CharField(max_length=120)
vote_count = models.IntegerField(default=0)
class ChoiceImage(models.Model):
choice = models.OneToOneField(Choice, on_delete=models.CASCADE)
img = models.ImageField()
class ChoiceColor(models.Model):
choice = models.OneToOneField(Choice, on_delete=models.CASCADE)
color = models.CharField(max_length=7)
I have a View that looks like this:
class CreateQuestionView(CreateAPIView):
serializer_class = CreateQuestionSerializer
With the following serializers:
class ChoiceImageSerializer(serializers.ModelSerializer):
class Meta:
model = ChoiceImage
fields = ('image',)
class ChoiceColorSerializer(serializers.ModelSerializer):
class Meta:
model = ChoiceColor
fields = ('color',)
class ChoiceSerializer(serializers.ModelSerializer):
choice_image = ChoiceImageSerializer(many=False)
choice_color = ChoiceColorSerializer(many=False)
class Meta:
model = Choice
fields = ('choice', 'choice_image', 'choice_color')
class CreateQuestionSerializer(serializers.ModelSerializer):
choices = ChoiceSerializer(many=True)
class Meta:
model = Question
fields = ('question', 'choices')
How do I create this constraint on my serializers? Also Am I designing this efficiently or is there a better way to do this?