Thanks! Those are all very good points. Great explanation of how color+saturation effects value. I love all the little light studies/notes/sketches in your sketchbook. I think it would be great if you could explain some of that stuff a little in here...
Good start, looks like you need to go a bit darker on your color.
Good job, looks like you're doing a lot of work. Proj. 4: leaving the lines on the spheres really cuts things up and flattens things out. From what I can see the light bouncing onto the spheres looks good, but the shadows don't look right. Also as stated earlier in the thread speculars arn't on straight line from the light to the object, they are refected off the objects surface to the vewer.
The Building looks good, The roof and the face of the small building on the left side are both too dark though. Also I would spend a little more time putting in the smaller elements (lots of value changes).
The spheres match well, the area around the core shadow on the color version is too dark though.