I know a person that can only see red clearly, so he shifts colors in the iOS settings to a red tint. Green icons shifted to red work fine, but what doesn’t work are the health and music icons which are white on red. Applying the color shift in iOS just turns these into red squares. This stuff is hard to get right. For him it’s better to not have single color icons with no outlines, but that’s the trend today. You might think less detail in icons would help accessibility but that’s not always the case.