Emojis are a standard and are actually unicode characters that is recognised and converted by devices as a smily face or a face with sunglasses, as an example, based on the unicode used. There's a technology group that works on this standard https://en.wikipedia.org/wiki/Unicode_Consortium. That Emojipedia site will tell you when that emoji was first introduced too.
My screen doesn't look like that when I'm typing an email. The smiley face is dark. I get the description here on this page when I hover over the emoji, having clicked on the white face between the triangle and the link symbol, but my 'Compose' screen looks like this:
The 'dark face' is the last symbol on the right.
