Creating Multiple Variations of the Same Animation - Scripting outside of AE?

Another solution would be using Plainly (plainlyvideos.com)

It would allow you to upload the project file into a Web App, parametrize it (select what elements you want to change) and then connect a data source like Airtable, Google Sheets, or API to drive the rendering. You could create a whole web app on top of Plainly and then simply use the API to send render requests.

Assuming the image dimensions and position don't need tweaking, then you can simply replace the external file on disc and re-open the AEP file. After Effects doesn't care if the contents of a file are different when it opens a project, only the filename matters. You could also create a simple text file (included within the project as a data object) and have your scripted controller read it to get the color values.

There's a bunch of ways to approach procedural projects like this. Here's a few of the most comment from simplest to most complex:

Essential Graphics / Master Properties:

Create a comp with those variable colors/text elements and use the Essential Graphics panel to add them to that comp's master properties. Now you can use the comp in multiple instances but with unique values. This requires a user to use the AE user interface.

Reference External JSON/JS file:

You can write expressions to reference an external sidecar JSON or JavaScript file that contains your variable info. You'd then have an external script like a BAT file on Windows or Shell Script on Mac create those JSON files, and then queue up the comp for rendering with the aerender command-line tool. This way you can automate the procedural process of creating the JSON file, duplicating the project, and queueing the project for rendering.

Web Procedural Rendering:

You can create a script or CEP extension (I would recommend an extension for this) that listens for changes on a web database or Spreadsheet and then creates and renders projects as needed as new data is added. When new data is received, the script can open the template project, update the variables, save out a new project, and then open and render or queue that comp for rendering.

If you're looking for an out-of-the-box solution for this, check out Templater.