[Can I pick a random color which are not in the image?]

That's unsafe (for me). There's a chance that I'll pick a color what already exists on the map. I need a precise color pick or something else what I can use in this situation.

[Can I pick a random color which are not in the image?]

Can you help me how to use it and solve my problem?

[Can I pick a random color which are not in the image?]

So, I'm working on a 2D game. There's an image where you can see the areas. Every area has a unique color on the image. (It wasn't made by me.) I want to add few more areas, but I don't know how to pick a color wich are not in the image yet.

Here's the image: https://imgur.com/yZYQzzv