Add a new colored glyph (from a .png) to a TTF font

FontCreator - Font Editor FontCreator - Discussion
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  1. FontCreator makes coloured fonts from layers. Each layer is a single colour. If the PNG has many colours it may take a lot of work. Four colours is not too hard. See the tutorial on Creating Multi-coloured Glyphs
  2. The emojji may be covered by copyright. If it’s your own creation or released in the public domain or opensource, there is no issue.
  3. I have no idea what limitations, if any, apply to fonts for Android.