Hi Jose,I can suggest you a few places but I do not know how far will they be to your liking ultimately. Still, if you are looking for colours in your photographs, you would probably love to visit the markets. In that respect, Chandni Chowk (Old Delhi) area especially the narrow lanes that house several shops selling sarees, salwars, fancy items for ladies is a must visit. But let me tell you that the area is very congested
But worth visiting. Moreover just some 50 or 100 metres away is the Red Fort from Chandni Chowk which I am sure you would be visiting (you said you will be visiting the monuments). Just make sure that you do not visit Chandni Chowk on Sunday (the market remains closed) and Red Fort remains closed on Mondays probably (I amn't sure though). Jama Masjid is also not far away.Janpath near Connaught Place, Dilli Haat at INA (near AIIMS), Sarojini Nagar, Lajpat Nagar, South Extension are a few other notable market places. India Gate, Lotus Temple, Red Fort, Qutub Minar, Purana Quila (Old Fort), Akshardham Temple etc, I guess, will be on your itinerary when you do the bus tour.
And if you wish to visit the old forts and structures of the Mughal times by yourself, you will find quite a few, though in somewhat dilapidated condition, in Hauz Khas (you will also get various art and antique markets here in Hauz Khas) and in areas around Mehrauli like Mehrauli Archaeological Park, Jamali Kamali Tomb & Mosque (some people say that this Jamali Kamali masjid is haunted though I have never seen or experienced anything spooky there. Still as a precaution, make sure that you return back from there before it's evening). You will also find Qutab Minar at Mehrauli. Humayun ka maqbara (Humayun's Tomb) at Nizamuddin and Lodhi Gardens at Lodhi Road (though now the Lodhi Gardens has virtually turned into a lover's point
, but it's a huge, humongous park and I am sure you will love clicking pics there. There too you will find a few crumbled structures from the Lodhi era inside the park). Some half a kilometre away from the Lodhi Gardens is the Safdarjung's Tomb which also is another often visited place.
There is a group on Facebook by the name "Secret Delhi",
https://www.facebook.com/groups/secretdelhi/ December is still almost a month away, so you may join this group and post your query there. I am sure you will get many more useful suggestions over there