Save multiple taxonomy terms in migration from array of tids

I'm having some issues with storing multiple taxonomy terms in a field as part of a migration.

I've created a custom plugin get_colors that returns an array of existing tids. A custom process plugin was needed her as the source values don't map cleanly.

pseudofield_colors:
    plugin: get_colors
    source: keywords

I can get a single tid value to work correctly but can't figure out how to iterate through this array and assign multiple values.

field_color:
    plugin: sub_process
      source: '@pseudofield_colors'
      process:
        target_id:
          plugin: entity_lookup
          source: target_id
          entity_type: taxonomy_term
          bundle: my_colors
          bundle_key: vid
          value_key: target_id

I'm lost in two ways:

1. What format should my return array be in? Should it just be an array of tids ["0" => "123", "1" => "567"] or does it need to have specific keys?
2. I found a lot of documentation on using sub_process and entity_lookup. Is entity_lookup necessary here? Returning a single tid works so I'd assume I could somehow iterate through my array and just assign multiple values but this is where I'm getting really stuck.

Thanks for the help!