png2cvs is a tool to create ColecoVision sprites from .png images with an alpha channel. It supports multi-color sprites (creating one ColecoVision sprite per color) and coordinate offsets so that big objects that require multiple sprites can be kept in a single file. Both 8x8 and 16x16 sprites are supported.
png2cvs is covered by the GPL. You can download the source of png2cvs 0.8 from 2017-08-08.