If everything looks right in composer, you might want to look into the TV settings. A lot of TV’s have a bunch of post processing, you’ll want to turn that off.
Check this article:
It could really depend on your needs and usage, but generally speaking, putting text in images isn’t a good practice, especially if you need to resize that image at runtime (pinch to zoom).
You might think about using a Text Asset on top of your image, and merge them in a group collection.
Again, it very depends on the usage. You might want to give us more precise examples?