If you want to store hex color code to a field, you can make use of the ColorField. It also provides a color picker, which can be used in the admin.

Simple add it to your color classes:

from django.db import models

from hvad.models import TranslatableModel, TranslatedFields
from django_libs.models_mixins import TranslationModelMixin

class Category(models.Model):
    color = ColorField()