i don't like too much use of one color. for example in this pic
http://www.envisionext.com/design/K%2001.jpg the stools, floor, blinds, cabinets, chairs and the thing on the ceiling are all basically burgundy. the same burgundy.
if i worked with one color, i'd use different shades of it - lighter and darker - to give more depth to the room.
i find this
http://www.envisionext.com/design/s%2002.jpg plain and very "decorator" looking, but not attractive. the pastels chosen don't spell comfort to me when mixed with the dark wood.
i guess while i like geometrics, i would usually prefer black, white, red and maybe a touch of blue for them, and i'd save the pastels and browns for something less geometric - but that's just my personal taste.