A new color can be inspiring without requiring a complete collection. A little experimentation with what you already own is a useful first step.
Look at your current palette
Arrange your existing products by color family and notice what you have overlooked. Try a small amount of a shade in a new combination, following the label for where each product can be used.
Make a considered addition
If a gap remains, consider a single versatile product or a sample rather than several near-identical shades. Think about texture and how often you will use it. There is no need to follow a color simply because it appears everywhere online.
Keep a simple record
Photograph combinations you like in similar lighting and note which products you used. This makes it easier to repeat a look and spot genuine gaps before shopping for another nearly identical shade.