Внезапно наткнулся в iOS-гайдах на интересную реализацию онлайна и оффлайна для людей с дальтонизмом
Be aware of colorblindness. Many colorblind people, for example, find it difficult to distinguish red from green (and either color from gray), or blue from orange. Avoid using these color combinations as the only way to distinguish between two states or values. For example, instead of using red and green circles to indicate offline and online, you could use a red square and a green circle. Some image-editing software includes tools that can help you proof for colorblindness.