I have a treasure counter text object. It's goldish yellowish. Every other text object I make has the same color. When I try to change the color in the inspector (they aren't parented) all text objects change color.
If I make it blue then my weapon counter, lives counter, and score counter all become blue. I even tried making another canvas but it still didn't work.
You are likely changing the color of the text material. This, as you've noticed, applies to everything using that material, you can either create more materials or more conveniently: use the Vertex Color property on the TextMeshPro object to set it for that particular object.
If you use vertex colors, you should set the material back to a full white as they will mix otherwise.