Yes, the following code will apply that color to a box:
Code:
import viz
import vizact
viz.go()
import vizshape
box = vizshape.addBox(pos=[0,1.8,4])
vizact.onkeydown(' ',box.color,[0.5,0.5,0.5])
You can press Alt + 1 in the Vizard editor to display a color dialog that inserts RGB values in the script for you.