Emoji are font-based, so it really depends on which firmware you're on... The 'stock' font for Android 4.3 is a black-and-white standard 'smiley' emoji, and the one for 4.4 is color, Google-hangouts-like emoji. However, manufacturers can change the font and display emojis differently; for instance, the Galaxy S4 displayed emojis in green, Android faces while the newer Samsung devices now show a more cartoonish, Whatsapp-like emoji. The code is the same, but how it looks like depends on where you're displaying that code (that's why most Macs can display emojis but not most PCs).