The picture above is Adidas CrazyTrain Elite Boost. Adidas Boost is a proprietary foam with great energy return. It’s very comfortable and extremely popular. You can find it in many models including UltraBoost, Pure Boost, Energy Boost, etc. In its raw form, Boost is white. Recent couple of years Adidas starts selling sneakers with Boost dyed black or other colors. Still, most Adidas shoes out there have white midsoles.
The same goes for Nike. Lunarlon midsole, according to Nike:
The Lunarlon midsole cushioning system consists of two parts
that work in tandem to deliver a light, soft, responsive feel.
LIGHTWEIGHT FOAM CORE: A soft yet resilient foam core spreads impact forces evenly over a large area.
FIRMER FOAM CARRIER: Stabilizes the softer core, holding it in place so it springs straight back up.
Therefore, it’s also a foam that’s mostly white, as shown in models currently available in the market. I have a Kobe XI Nike ID:
Although its outsole is not white, the actual cushion, which is a drop-in lunarlon midsole, is indeed white.
Another example of a white foam: Asics Gel-Kayano 23.
The conclusion is clear. Sneaker outsoles are mostly white because the material is foam. However, white gets dirty easily when there’s dust and mud. Personally I don’t like white outsoles. I feel compelled to clean it every time my shoes get dirty, or when it’s raining. Adidas recently starts selling Triple Black Boost models, which feature dyed Boost midsole. Too bad my CrazyTrain Elite Boost does not come with that colorway!