Free font editor which lets you create vector graphics and export TTF, OTF, EOT and SVG fonts.
OpenType-SVG color fonts is a rather new format and some applications does not support it. Mozilla Firefox and Microsoft Edge has support color fonts in their browsers but Chrome lags behind at this point. Creating monochrome fallback glyphs can take a long time if your glyphs contains many small parts (hundreds or even thousands). In addition will glyphs with too many details hardly fit on the TTF grid. You can get around this problem by creating an empty fallback glyph and importing a monochrome version with less details of your colored letters.
Alternates provides a way to put several glyphs on the same Unicode character and selecting which glyph that should be displayed when the font is used.