You can get just plain neopixels from adafruit, and run them from the Arduino that you have the motor shield attached to. Connecting a circuit playground board to a uno will introduce a whole slew of additional complications. On the other hand, if the motor driver is a separate board you might be able to connect it to the circuit playground directly.
Maybe give us all the information requested in the "How to use this forum" post, and you'll get more than shot in the dark guesses.