Support Foreground and Background Colors

Right now the colors are hard coded to black background, white foreground. I experimented briefly with changing it and found that some of the emoji seem to render without a "transparent" background so it makes black blocks surrounding those emoji. When the background is black it blends in and looks correct.

Need to check these files and their palette to see if they're configured for transparency and whether some issue within imageload may be causing it not to work. A good place to start will be comparing raw contents of the PNG file on one that currently works with one that doesn't.

Start by comparing the raw contents of a working PNG with one that renders incorrectly, then inspect the referenced palettes and imageload behavior for transparency. Done means foreground and background colors can be changed and emoji no longer show unwanted opaque blocks.

Written by the indexing model from the issue text.