Can't figure out the correct payload to BatchGetItemCommand in aws-sdk 3

Question

I can't figure out what the payload should be for BatchGetItemCommand. I've read the docs (https://docs.aws.amazon.com/sdk-for-javascript/v3/developer-guide/dynamodb-example-table-read-write-batch.html) and looked at the Typescript typings.

This is the table:

    StagesTable:
      Type: AWS::DynamoDB::Table
      Properties:
        TableName: ${self:service}-${opt:stage}-StagesTable
        AttributeDefinitions:
          - AttributeName: color
            AttributeType: S
          - AttributeName: stage
            AttributeType: S
        KeySchema:
          - AttributeName: color
            KeyType: HASH
          - AttributeName: stage
            KeyType: RANGE
        ProvisionedThroughput:
          ReadCapacityUnits: 1
          WriteCapacityUnits: 1

I am trying to retrieve the two rows where the color is blue or green. This is my payload

  const payload = {
    RequestItems: {
      tableName: {
        Keys: [
          {
            color: { S: 'blue' },
          },
          {
            color: { S: 'green' },
          },
        ],
      }
    }
  };

I get

(node:79852) UnhandledPromiseRejectionWarning: ValidationException: The provided key element does not match the schema at deserializeAws_json1_0BatchGetItemCommandError (.../node_modules/@aws-sdk/client-dynamodb/dist-cjs/protocols/Aws_json1_0.js:589:24) at processTicksAndRejections (internal/process/task_queues.js:95:5)

What am I doing wrong?