It is often easy to get lost in a sea of data points. However, by utilizing different sizes and colors of points, you can create contrast which allows the reader to focus on a particular set of data.
Big thanks to our friends at Cartastrophe for inspiration and this great diagram:
Figure 1. Is it easier to spot the small cluster of squares near the center, or the cluster of triangles? It is clear that size allows for greater selectivity than shape in this example.
Figure 2. The use of size, color, texture, and shape are used to encode information, as well as, to create greater contrast. In the above figure, the use of bright red color allows the reader to focus even faster on the cluster of small squares.
Figure 3. If trying to increase focus on one particular set of data, consider changing the color hue, value, or intensity of the surrounding data to further increase contrast. The figure above illustrates that color hue contrast can be more selective than subtle color value.