Mine also come when called, to a bucket. They don't care what colour it is either. My dog is too old now to gather sheep.
I have a long 'catching pen' which leads into a short one, and then that empties into a race, which runs back along the side of both pens and empties back into the top of the long pen.
When I call them, I have already scattered food into the short pen, which they know. So they run into it, I shut the long pen gate to the field, push them down into the short pen, and sometimes then through into the race, depending what I'm doing.
The pens and race are made of wooden hurdles, tied with baler twine to wooden fence posts knocked into the ground.
Mine are Shetlands - I can gather them once a fortnight, perhaps once a week for a couple of relatively-untraumatic things. Any more often than that and they get wise and wary.