Using style attributes

The documentation for Drawing API in Drupal 5 is what I'm basing the docs and development of a GD toolkit and further stuff in Drupal 6.

I have spotted that in the documentation it mentions that every shape has this:

Style attributes: #stroke, #stroke-width, #fill, #opacity

However there are no examples given of what this is. I found via drawing_demo that #fill is a color value - but still there is no explanation of what possible color values there are, for example can you supply a color as "#fff" as well as "#ffffff" and "white" and what about "rgb(255, 255, 255)" ? What sort of value is expected in opacity? Is it 0-255 or 0%-100% ?
I can find no information about expected values for #stroke and #stroke-width, and I wonder perhaps for some elements like 'line' this would not even have an effect?? I don't know I'm not all that familiar with SVG.