Good accessibility labels are at the core of good accessible apps. It should be a localized succinct string that tells as much as possible about the component (without including its type) and provides context avoiding verbosity and redundancy.
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Sometimes, buttons change meaning, for example when toggled. An example is a play button, tap it and it becomes a pause button. In such case, updating its accessibility label will be clearer than trying to convey the change with traits or values.
Images can automatically scale for accessibility content size categories, by setting the adjustsImageSizeForAccessibilityContentSizeCategory property to true, for any UIImageView you'd like to get its size adjusted. https://developer.apple.com/documentation/uikit/uiaccessibilitycontentsizecategoryimageadjusting/adjustsimagesizeforaccessibilitycontentsizecategory
You should convey important information in multiple modes, not just color. If you are still required to do so, at the very least you should complement that info with other modes, like symbols, if the user requested differentiation without color.
