Hey,
You can have the bright dot (red, yellow, green dot..) and the dark dot (black dot), and the whole cycle from the afterimage to the bright dot and dark dot with your eyes open, if you let it to develop. Actually you can have all of the visuals that you see with your eyes closed with your eyes open too. Although it seems that it's different for different people, on how long it would take to bring the visuals to the eyes open space, but I guess the sooner you start practicing with your eyes open, the better. I think the easiest way is to start practicing with eyes open in a dark room, and try to see the afterimage and the dots in the space in front ot you, then do it in a room with dim light, then do it with full lights on.
Another trick is to use bright and dark surfaces, like a wall, or a blank sheet of paper or a black/dark surface in front of you, to see the afterimage and the dot on it, or try to see the dot in the palm of your hand in a dim room, and gradually let it to develop.
It could happen that sometimes you see the dot with your eyes open, but don't see it with your eyes closed, and vice versa, it's natural.
For me, if I stare on a candle in a brightly lit room, then the color of the dots changes, and instead of having a red or yellow dot, it's magenta, green and deep cyan. All of the visuals that I see, with eyes open or closed, are exactly the same, the only difference is that, with eyes open in a bright room, the colors are less defined because there is more light.
Another point is that, after doing this practice for some time, especially if you do it with eyes open too, the whole perception of visuals changes. There is more vibration, beauty, aliveness and spaciousness/volume in the visuals, so just looking at external sights can be a fascinating practice.
I'd also use white clouds on a clear sky as the kasina object, and that would create beautiful afterimages, and affect the colors in a good way.
And a good point from Daniel to use when walking, is to focus on how the perception of space changes when you enter from one space to another, like walking from one room to another. The whole perception and imagery of the internal space changes in that transition.
Good luck!
