I've had a cold for about 5 days with as cough & mucus. In the morning the mucus is dark green & the cough is NT getting any better. Should I go in?

Cough + cold symptom. It would be difficult to determine what is causing this without being seen. Green mucus can occur in the morning naturally as a cold is resolving and does not necessarily mean there is an infection. If you have a fever or the symptoms last longer then 10 days then you should see your doctor. You can try saline nasal spray and Mucinex (guaifenesin) to loosen the secretions if there is no fever.
Need antibiotics. Sounds like you have developed a bacterial bronchitis. Sometimes is can start as a viral infection which then develops into a secondary bacterial superinfection - i would recommend seeing your doctor for evaluation and probably rx for a course of antibiotic.
See doctor... Sometimes, as a cold infection resolves, the cough can worsen due to bronchospasm caused by the airway inflammation. The treatment for this can include bronchodilator and steroid inhalers. These are prescription meds so see your doctor to determine the cause of your ongoing symptoms and so the proper treatment can be initiated.