Yellows mean you don't care about privacy (a big company doing legitimate business may not care), or have accepted that blockchain analysis will defeat your privacy efforts anyway (https://en.bitcoin.it/wiki/Privacy), or you're a novice bitcoin user who doesn't understand what is safe and what is not

High frequency speculative trading could explain the pre-confirmation transactions. Maybe the probability of double-spending is so low, and the chain consensus is so strong, that a transaction in the mempool (before being locked into a block) is good with high probability. Or it could be novices who don't understand the danger

Definitely the Bitcoin network looks unusually "hot" today