This design turned out quite good I feel, and it was quite easy to do.
First I painted all nails in 2 coats of my lighter colour. In this case it was a pastel peach/orange.
Then I painted half of each nail with my darker colour. In this case I used a coral/dark orange colour.
Then once that was dry, I used a large sized dotting tool to place some of the lighter coloured dots on top of the darker colour. I made sure they were placed along the line where the two colours meet though and that the dots were touching into the same colour on the opposite half of the nail. This made it look like the lighter colour was running into or dripping down into the darker colour.
I then repeated the same but for the opposite colours. I made sure the dots were placed along the line where the 2 colours meet, but that they were in between the gaps of the dots on the opposite side. This resulted in everything looking like it was melting into each other.