With content ready to go in your After Effects timeline, create a circle using the shape tool in the center of your composition.
To do so, click and hold down the Shape Tool, and then select Ellipse. Set Fill to Red, and set fill to none.
By holding Ctrl+Shift, click and drag on the composition to create an even circle.
Create two Scale Keyframes by selecting your shape layer, click the “s” key to open up scale properties, and then create one keyframe at the beginning, and the second at the 2 second mark.
Adjust your keyframe values so that your first keyframe is set to 0%, and the second is at around 350% (or large enough to fill up the composition).
Select both keyframes, make them Easy Ease keyframes (Click F9 or right click on keyframes, Keyframe Assistant, Easy Ease)
Open up Graph Editor, turn on Value Graph, and set value so that the animation gradually enters to then eventually speed up.
Next, go to the Effects and Presets menu, search Drop Shadow, and apply to your shape layer. Here are the following values I used - Opacity = 80%, Distance = 0, Softness = 75.0
Rename layer by selecting layer and click Enter on your keyboard. Label layer “Red”.
Duplicate layer, and offset by 10 frames (can hold Shift and press Page Down to jump ten frames in the composition.) Adjust color to orange.
Repeat step 8 until all colors have been used.
Duplicate the final shape layer (in our case the “Pink” circle), offset by 10 frames, rename the layer to “Reveal”, and leave as is for now.
Select all color layers, click Ctrl+Shift+C to Pre-Compose layers.
Apply “Alpha Inverted Matte to Reveal” to the Precomposed layer. Select both the Reveal layer and Precomposed layer, and line up to your images in your timeline.