So many differences, at a glance.
Pink Luna - has monotonous hair, coat is a shade or two darker than Cadenza, has monotonous wings, doesn't have a full outline of her eyes, has a completely different hairstyle, has blue eyes, has a slightly different wing style, has a longer horn, doesn't have her wings going over her frame.
Cadenza - has tricolor hair, coat is a shade or two lighter than Pink Luna, has gradient wings, has a full outline of her eyes, has a completely different hairstyle, has purple eyes, has a slightly different wing style, has a shorter horn, and has her wings going over her frame.
From a glance. Upon deeper investigation, I'll probably find more differences.