Very happy that Vanda Kiwi Bob is flowering for a second time this year. The spikes are about a month apart. The darker bloom opened yesterday - it looks like two different plants
Some flowers fade over time, some actually intensify color with time, and differences in temperature and/or light level can affect flower color at different bloomings.
I'm guessing that color from one parent develops first, then the other one becomes stronger. In other orchids, pink/red (which tends to develop later) can "wash out" yellow, leading to lighter or even white. (Like Paph. Armeni White, but can occur in other genera too) I wonder if that's what's gong on here.