I have studied with both Elio Camacho and Ovanes Berberian. Both are among the best colorists available anywhere and both give extremely impressive demos. Ovanesís demos are typically several hours long, late at night, and without instruction. Studentís paint during the day and his instruction consists mostly of very insightful critiques of student work while it is in progress. Most students simply follow Ovanes from easel to easel to hear his daily critiques.
Elioís demos are en plein air and he actually prefers for students to ask questions as he demonstrates. Demos are often accompanied by a brief lecture. In addition, Elio is available throughout the day and spends a lot of time one-on-one giving instruction particular to each student. Elio has a workshop scheduled for Napa Valley California October 1-5, 2012 (http://www.eliocamacho.com/theStore/home.php?cat=257
). I highly recommend it to anyone interested in learning to really see color en plein air.