I just do it in post with inpainting. Set the scene with the original generation, then inpaint each character with their description.

Hello, I use brackets around each individual, including their special hair...example:
---
2girls, (Pia, girl, green hair), (Mia, girl, red hair),
---

and so on for other differences.
Works most of the time but sometimes SD will make a wild move, however careful we prompt...!
https://civitai.com/images/21190330

This is a year old, but regional prompting (a A1111 extension) is the most reliable method. It's got a bit of a learning curve, but it lets you break an image up into sections where each area can receive their own prompt (along with a common prompt that applies to all of the regions).

So, in this case, you'd probably cut the image into halves vertically, and then you could put "rainbow hair" in one section and not the other, and it would only apply there.

For Forge you can also use Forge Couple. It's similar to RegionalPrompter but it's working with Forge and Pony.

@Pressydent hello...I have the Comfy Couple, how can I find this Forge Couple...?
Greetings

@jakobhovman259 Afaik it's only useable for Forge AI. If you are using Comfy I think you can't use it. There you can download it from the "Extensions" tab => "Available"

@Pressydent Thank You , not so great at adding extensions yet.
Found it via Google:
https://github.com/Haoming02/sd-forge-couple.git