Make a cytoband data store class that can download and parse (just in memory) a cytoband file, and emit features from it. It's basically a dialect of BED. The features produced should have the same tags as those produced by loading a cytoband GFF like that described on http://search.cpan.org/~lds/Bio-Graphics-2.33/lib/Bio/Graphics/Glyph/ideogram.pm into an NCList.
Make a FeatureGlyph that draws the bands as colored regions.
cytoband file format: http://www.broadinstitute.org/igv/Cytoband