reset "s" in points3d

Hi,
I have series of pointcloud frames which I am animating using mayavi
the number of points changes with in each frame.

I can get the anim to work using reset on x,y,z but I dont know how to reset the
"fourth array s of the same shape as x, y, and z giving an associated scalar value for each point,"
which gives me the color value.

Appreciate your help.

thanks