I've been using my wok for about a year now, and recently it's developed a kind of patina around the bottom of the cooking surface.
I've tried to follow the care instructions as best I can, taking care to wipe it down after use, and only scrubbing it with cleaning fluid when it gets really dirty. If I have to scrub it down I typically wipe some oil over it whilst heating very gently in order to "re coat" the wok. I don't know if this is typical wok care procedure, but I'm following the care guide that came with this particular wok.
The wok is made of cast iron, and is sold by Le Creusset, information here.
The patina has gradually become more noticeable over time, but it is not flaky, cannot be removed easily by scrubbing and/or washing up liquid. It doesn't impart any kind of negative flavour into the cooking, so it hasn't put me off using it.
Does anyone know what this is, and how best to remove it?