Hi Horace,
check this screenshot : http://www.activeworlds.com/newsletter/ ... er4_lg.jpg
Inside the bottom blue rectangle (ignore the red rectangle), there is the green color picker; right under the green color picker is a button called "setvcol", this is the one you want.
Also, at the right of the upper blue rectangle, you will need to click the "orange rectangle on green square" button so that you can select which faces are affected
Just one little caveat : STK does not support sharp changes in vcolors like blender does, so make sure to smooth any vcolor so that the color is the same on all sides if a given vertex (or split the faces if you wish sharp effect)