I was having a similar issue:
Running "flutter packages get" in austin-feeds-me-flutter...
The current Dart SDK version is 2.0.0-dev.58.0.flutter-f981f09760.
Because austin_feeds_me depends on palette_generator any which requires SDK version >=2.0.0-dev.61.0 <3.0.0, version solving failed.
pub get failed (1)
Process finished with exit code 1
I fixed it with the following commands:
flutter channel dev
flutter upgrade
Fix source: https://github.com/flutter/flutter/issues/19382