I just did a quick google search of relationships between color and emotion. I found the following quote:
"The color green elicited mainly positive emotional responses, including the feelings of relaxation, calmness, and happiness as well as comfort, peace, and hope. This is somewhat in agreement with the findings of Saito (1996), whose subjects found green to be refreshing and beautiful. Reasons given for positive responses to green showed that green was associated with nature, grass, trees, and reminds someone of outdoors and springtime, consistent with Hemphill's (1996) findings. Similarly, Saito (1996) noted that some of the Asian subjects who preferred green indicated the positive feeling about the color because of its association with the image of a forest."
The source is here:
http://findarticles.com/p/articles/m...n6249223/pg_4/
Given this I would do a quilt for his waiting room in soothing shades of green. A bargello is indeed an excellent choice because you can put so many different shades of green in one quilt. I just ordered and received the book "Bargello Quilts with a Twist" by Eileen Wright. Lots of good ideas for Bargellos in there.