We will have a look at light behaviour and at some rendered images. Understanding transparency will help you in drawing transparent objects, but it will not make it any easier. For more information about light and colours, see the F.A.R.P. index about Color . Our light source is at the top left . Make a darkening gradient towards the light source .
Most transparent objects are somewhat reflective as well.
I would advise not to draw any reflections, because they distract the viewer too much. If you do want reflections, add them now. Be sure to keep them transparent. Highlights are the only necessary reflection I would put in. Put a second highlight opposite of the first highlight.