Well, if you didn't already know, Copper and Ariel are EXTREMELY different.
Their only similarities being their eye color and species.
BUT!
Would you like to know their MOTHER?
She's actually rather important to the original show, and has few speaking lines.
Another tiny hint, she's become a Brony favorite character to display!
NO MORE HINTS!
Guess at your own risk! JK, but you know :D