Ukramedia Has a Look at Creating a Rig That Will Let You Pick Colors By Moving a Null Around the Scene
Ukramedia’s Sergei Prokhnevskiy shows how you can create a color picker effect in After Effects. The setup uses expressions and a null that will change the color of an element based on what is underneath the null.
This lets you simply move a null in the scene to change the color of an element, such as in the example, a logo. This is thanks to the sampleImage expression in After Effects. sampleImage can read color and alpha information of a layer and return values for those. You can then use those values to drive something else. With Sergei’s example, he is driving the colors of a target layer.
This technique is nothing new. In fact Dan Ebberts wrote about using the sampleImage expression to access layer color, years and years ago.