Julet (or Juliet) connectors are common on many e-bikes because they offer a tight, waterproof connection. There are quite a few different types based on the number of pins, but they all look similar and connect/disconnect in the same fashion.
The plug color depends on the number of pins in the connector.
A Julet connector is generally pretty tight because of its waterproof design. They come apart by pulling, NOT TWISTING. You want to refrain from twisting or wiggling the plug while disconnecting so as not to damage the pins or the colored plastic of the plug. Note the arrows on the outside-they help align the connectors so the pins are not damaged.
To connect a Julet connector, align the arrows on the outside and push them together. Start gently until you feel the connector align and then push together to seat securely. There should be no colored plastic showing when it's connected properly.