How can I optimize updating Objective background colors from the Color table and manage historical changes?

I have a grid display of boxes where each box’s background color is determined by a value in the Objectives table. The Color table holds the hex colors corresponding to that value, so updating the Color table affects the program globally. I'm using a column sled value instead of just an ID so that I can reference the color easily without tracking row deletions.

I update the Objectives table by looking up the corresponding color in the Color table. Here’s the current approach:

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objective_num = Objectives.objects.filter(dashboard=dashboard_id).values('id','objective_color')  # get dic of latest color values for each id
for n in objective_num:  # Iterate over all the objectives
    color_hex = n.get('objective_color')  # get color code to use to get corresponding hex value from Color table
    obj_id = n.get('id')  # get objective id for the color
    color = Color.objects.filter(value=color_hex).values_list('objective_background', flat=True)  # get color hex value that matches the color set in Objectives
    Objectives.objects.filter(dashboard=dashboard_id).filter(id=obj_id).update(objective_background=color)  # update color hex in Objectives table

I have two questions:

1. While this method works, it feels excessively heavy. Is there a more efficient way to update the Objective background colors when the values change?

2. Although I only need current values right now, I might want to store historical data in the future. I'm considering two approaches: adding a new column for each update (an Excel-like approach) or inserting new rows with each update and numbering them. Which method is more suitable for tracking historical changes?

Below are simplified versions of my models:

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class Color(models.Model):
    color = models.CharField(max_length=10, default='White')
    objective_background = models.CharField(max_length=7, default='#FFFFFF')
    value = models.IntegerField(default=1)
    def __str__(self):
        return f"{self.color} (Hex: {self.objective_background}) is color number {self.value} with ID {self.id}"
    
class Objectives(models.Model):
    user = models.ForeignKey(User, on_delete=models.CASCADE)
    dashboard = models.ForeignKey(Dashboard, on_delete=models.CASCADE)
    objective_background = models.CharField(max_length=8, default=1)
    row = models.ForeignKey(Row, on_delete=models.CASCADE)
    objective_position = models.IntegerField()
    objective_color = models.IntegerField()  # Used to store status color based on performance
    objective_text = models.CharField(max_length=1000, blank=True)
    timestamp = models.TimeField(auto_now=True)
    def __str__(self):
        return f"Objective: {self.row} {self.objective_position} {self.objective_text} at {self.timestamp}"

Any suggestions or improvements would be appreciated.