White midsoles, have a tendency to yellow over time. There are many reasons or factors why they yellow, but the basic theory is that direct sunlight breaks down those chemicals used to create these bright white midsoles. There are a few ways to unyellow them, but if you have tried almost anything and unable to get it done. Fear not, because CPB Customs has a way to keep them looking brand new again.
Here's one of his works this year with the most noticeable improvement. Check 'em out!