Periwinkle belongs between the pinks and blues in a mixed manicure. It gives the two sides a shared purple note.
Some pastel sets look split into a warm hand and a cool hand. A blue-violet nail helps the two halves feel related. Secret Peri-Winkle by China Glaze is a polish option for that middle ground. Keep the neighboring pink light enough that it does not overpower the blue. Finish with the same top coat across the set so the surfaces catch light together.