It's all about the reflection of light. You can either add mirrors at strategic points, obviously combined with small bathroom paint colours, and get a bathroom that feels lighter, brighter, and more open. 

Let's come to the bathroom colours now. If your bathroom doesn’t get a lot of sunlight, lighter bathroom paint colours like white, off-white, or light grey will help. If you prefer darker colours, stick to small sections or an accent wall rather than painting the entire bathroom in dark bathroom paint colours.