RE-DO

 I don't confide ALL the mistakes I make when learning things, 

but there is an essential element to be appreciated in Sketchbook.

Do not skip this step in coloring an object:

                                                       

Here, the object is taken to black and then colored in the desired shade. 

I initially did a perfect sphere replica only to find, down the road, that the

black shadow underneath the sphere was not showing up behind the image, although

everything was set up for it to do so: ie in a lower layer, and the sphere at 100%

opacity. 

I had colored it with the Air Brush tool on white...

Only to conclude that Air Brush is always partial cover!!!

Had to re-do the whole thing, using a paintbrush tool.