Show color picker in talk-throughs

Students get confused because we don't show the color picker in talk-throughs. It'd be great if we could show it popped up and even show how the color changes inside it (we'd need to do some interpolating or discrete jumps, since we don't record every mouse move).

Start by locating the talk-through implementation and the code that handles the color picker. Determine how talk-through interactions are recorded or replayed, then add a visible picker state and color transitions during playback. Done means students can see the picker open and observe its color changing without requiring every mouse movement to be recorded.

Written by the indexing model from the issue text.