Draft: Possible workaround for lack of rgba color support

Possible fix for issue #419 (closed).

@doctormo review requested, please. Specific points of concern:

(1) It seems like it would be better to compute the rgb and alpha once on run, rather than once per object as it appears to be here. I haven't been able to quite get it right, trying to do so.

(2) Can you show me how to add appropriate test cases?