{
  "builders": [
    {
      "type": "docker",
      "image": "ubuntu",
      "commit": true
    }
  ],
  "provisioners": [
    {
      "inline": [
        "echo hello"
      ],
      "type": "shell"
    }
  ]
}

docker output will be in this color.

==> docker: Creating a temporary directory for sharing data...
==> docker: Pulling Docker image: ubuntu
    docker: Using default tag: latest
    docker: latest: Pulling from library/ubuntu
    docker: Digest: sha256:30e04ddada6eb09c12330c7df72cad1573916c7100168c34076808169ff6d805
    docker: Status: Image is up to date for ubuntu:latest
==> docker: Starting docker container...
    docker: Run command: docker run -v /home/mike/.packer.d/tmp/packer-docker164405582:/packer-files -d -i -t ubuntu /bin/bash
    docker: Container ID: bbb118b6d47278b0d1cb22dfcad4d88defa0667bd2ac42b8cdac974ac7e21681
==> docker: Provisioning with shell script: /tmp/packer-shell625042236
    docker: hello
==> docker: Committing the container
    docker: Image ID: sha256:955a4251f96c6198b27dd0a4fd36de4a0868f7351e0e115d0df8ce466ce83676
==> docker: Killing the container: bbb118b6d47278b0d1cb22dfcad4d88defa0667bd2ac42b8cdac974ac7e21681
Build 'docker' finished.

==> Builds finished. The artifacts of successful builds are:
--> docker: Imported Docker image: sha256:955a4251f96c6198b27dd0a4fd36de4a0868f7351e0e115d0df8ce466ce83676