Questions and postings pertaining to the usage of ImageMagick regardless of the interface. This includes the command-line utilities, as well as the C and C++ APIs. Usage questions are like "How do I use ImageMagick to create drop shadows?".
In general, a background colour can be applied where there is transparency. In this particular case, much of the image is "hidden" by transparency, so one of the options that makes the pixels fully opaque is more appropriate.