Is it possible to decorate elements of a collection?

I have a collection called sections that contains red.html, green.html, and blue.html, which I want displayed in a list in that order rather than in alphabetical order. I could add a field called order to the front matter of each, with the values 0, 1, and 2, but then if I decide I want to add a page orange.html in between red.html and green.html, I would have to edit green.html and blue.html to change their numbers. Since I’m actually going to have lots of pages and be moving them around fairly often, I don’t want to do this. Instead, I would like to define a list in _config.yml that specifies the order of the collection elements:

- /red/
- /green/
- /blue/

(where for convenience I’m listing the pages’ permalinks - I could use anything else that’s unique per page). If I was writing in Ruby or some other language, I would then use the “decorate-and-sort” pattern to sort the collection pages:

  1. Create a hash from permalink to sequence {'/red/': 0, '/green/': 1, '/blue/': 2}.
  2. Loop over the collection pages and add an ordering field to each by using the page’s permalink to look up its sequence number.
  3. Sort the collection using the ordering key.

I want a solution that will run with GitHub Pages without any plugins, so is there a way to do this in pure Jekyll? Thanks.