I host various workshops depending on what the organization is looking for. Here are some examples.
Blindfold painting (this is the most typical)
in this exercise participants paint blindfolded on paper pre-prepared with raised line drawings using paint that has a different texture for each color.
There are lots of different exercises that we could do with clay; it is a great way to experiment with form and texture. Scents can also be added to help distinguish colors; this also seems to work well with people dealing with Autism and Alzheimer's. 
Drawing/painting or molding clay by using touch alone to investigate subject. Boxes with a hole in them just large enough to fit a person's hand and then an item or items are placed into the boxes that are textually interesting. This is a great way to shift the emphasis away from the eyes and start engaging the other senses. 
Taste for color
Color can be a great tool to express feelings, emotions and ideas. All to often we think of the color of an object in objective terms - whatever shade it is from the light reflecting off of it. This exercise helps to broaden our ideas of what color can mean to an artist, and how it can be used to express different ideas. Jelly Belly jelly beans are an easy and inexpensive way to add flavor for this workshop. Each participant can be given some jelly beans, and the flavors they taste dictate the colors they will use in their painting.
Music inspired activity
This is another activity that encourages participants to think of color in other ways. This helps quite a bit when it comes time to do a verbal description of a painting - thinking creatively about color can be an aid when it comes to describing art so that its emotional qualities can be relayed as well. There are many different ways to do this activity. The participants can try to capture the overall feel of the music in their art, or the rhythm, or beat. In one version a song can be played several times - each time a different component is added. First just the piano, then the entire band, then the singer is added, and lastly the crowd. Working on a painting with each component being added separately helps us to understand how each part is affecting our thoughts and emotions, and how this effects the art over all. This workshop is nice to do too when discussing artists that used music in their work such as Kandinsky and Mondrian. 
Painting workshop
This is a longer workshop in which the participants actually complete a painting from start to finish. The workshop is taught in such a way so that artists from beginners to experts can follow along and feel challenged, but not overwhelmed. This workshop is also conducted in a way so that people of all abilities or disabilities are able to participate and contribute. The goal here is to relax, have fun, and make some art!