Emoji on the Microsoft SwiftKey Keyboard uses the standard Android font. This means, that depending on what version of Android your device(s) are running and what app you are using, the look and color of the emoji will be impacted.
Some apps, such as Facebook and WhatsApp, have built in their own variations of emoji that are different from the Android system font.
This means that if you use a Microsoft SwiftKey emoji on Facebook, for example, it will look different in the app compared to what you saw in Microsoft SwiftKey Keyboard. This is not a bug, but something implemented by other apps. Also, if you send messages from an Android device to an iOS device (or vice versa) the emoji may display differently.