A quick video overview of how to create color swirls, look further down for a video on the editing
Pour small amount milk into white shallow bowl, you need less than you think, it only needs to be about a centimeter deep
TIP: pour milk slowly down the side of the bowl otherwise you'll end up with bubbles that you have to pop
Drop food coloring into your milk, make your drops somewhat close together
Swirl colors with a small pointer, stick, tool, whatever you want, q-tip even
Drop in your dish soap overtop the center of your color swirl, clear dish soap works best visually
Swirl with your pointer until desired results, unfortunately adding more soap will not reproduce the "swirling" results
To create images with a black background instead of the white of the milk, you can use either
Image > Adjustments > Curves
Preset > Negative (RGB)
Image > Adjustments > Invert
which each give different results.
Often times after this step you have to play around with the hue under
Image > Adjustments > Hue/ Saturation
to get an appealing color palette.
Some cropping & toning