Solution:

    @api.model
    def cron_andon_color_set(self):
        contracts = self.env['account.analytic.account'].search([('x_contact', '!=', False),('date_end','!=',False)])

        for record in contracts:
            current_date = fields.Date.today()
            end_date = fields.Date.from_string(record['date_end'])
            difference = int((current_date - end_date).days)

            if difference >= 0:
                #We have passed this date
                record['x_color'] = 1
            else:
                #In the future
                flipped_difference = difference * -1
                if flipped_difference > 90:
                	#More than 90 days
                	#Blue
                    record['x_color'] = 4
                elif flipped_difference <= 90 and flipped_difference > 60:
                    #Between 90 and 60
                    #Green
                    record['x_color'] = 8
                elif flipped_difference <= 60 and flipped_difference > 30:
                    #Between 60 and 30
                    #Orange
                    record['x_color'] = 2
                else:
                   	#Less than 30
                    #Red
                    record['x_color'] = 1