This is one of my favourite freehand nail art ideas. I think this picture is similar to watermelon. I paint background with different color varnishes and add acrylic lines after that.

You need:

Light green varnish

Pink Varnish

Green, yellow, orange and black acrylic paints

Thin brush

Top coat

Draw spots with green and pink varnishes.

Now outline these spots with green, orange and yellow paints.

Outline with black and add dots.

Finish with top coat.