OK I have seen that look on indoor shots with no flash. It seems to be a combination of white balance settings combined with underexposure in low lighting conditions. Your lack of sharpness may be due to longer exposure times.
If you are shooting indoors with only normal room lighting you will need to use a flash, almost 100% of the time.
working on it in Middle TN Nikon D3100 18-55 mm Nikkor VR 55-200 mm Nikkor VR 55-300 mm Nikkor VR 150-500 mm Sigma OS