There’s definitely a ‘right’ way to make the most out of this ingredient. When you choose a vitamin C serum for the face, there are a few things to consider in order to choose an effective formula that’s going to get you real results. Generally, your vitamin C serum should be a light-yellow colour, or completely transparent - if it becomes dark yellow or brown over time, that’s a sign that it’s oxidising which means it’s likely to be less effective.