color: simplify factory design

Supporting other factories in independent protocol extensions was a nice idea, but complicates the design for questionable benefit. The existing design was only half of it, too, because wp_image_description_v1 interface had events related to all factories instead of the factories having their own events.

Therefore go back to a simple monolithic design, but keep the different factory requests still optional and discoverable.

This gets rid of the new_id interface hack.

There is also a little bit of unifying the wording, and couple typo fixes.