Font rendering has always had to adapt to colors. There were (non-standard) multi-color fonts in the 8-bit era, too. It's not just emoji that are using OpenType color tables and OpenType color tables are not the only way that colors in emoji have been handled, just one of the most standardized/algorithmic methods. Part of why they were standardized is how much they resemble other tables needed for complex ligatures in other languages that aren't emoji. Emoji didn't invent complex ligatures with multi-table lookup to render. Emoji benefit from simple extensions of the exact same mechanic. It's a new table, yes, but it is not a complex table, it's one of the simplest tables in OpenType.