Ivano, some folks argue to use some ambient light to keep your eye tuned to Jupiter's brightness and the eye at photoptic(?) sensitivity. But, I find ambient light to be distracting as I observe with both eyes open (one covered.)
I do as you do, let Jupiter burn into my retina, then click on a flashlight (so you can actually see the paper) to sketch a detail. Turn it off, the readjust to Jupiter at the eyepiece. Maybe ambient light works, dunno, but I prefer to block ambient light and just focus on the subject.
Yea, it's amazing to look at a star and be 'blind' in one eye because Jupiter has killed dark adaption.
Both eyes are open and relaxed, one is just covered looking at blackness in the palm of my hand or an eye patch. I think this helps both eyes relax, or maybe just allows me to relax. With both eyes open, you can kind of pretend you are using them both to observe Jupiter. That's a more natural condition.
Keeping ambient light might help color perception to some extent, until the cyclops eye is adapted to Jupiter. Anyway, yes, a flashlight does not produce sunlight where the eye is naturally adapted. So, who knows, really, what affect a flashlight has on color perception. Interesting point and maybe one of those fine, refined techniques for experts to use. Get a sun lamp.
Replicating color accurately is always difficult. With crayon it's a bit easier, less to choose from.
With a billion color PC pallet, it can be a real bear to get it right. Then, matching the hues to every monitor on the planet is pretty tough, too.
But, yes, Jupiter does have some yellow on it so to portray it with yellow is correct. And some white. By the way, you captured 2 hues in the SEB, that's a feat sometimes, especially when you are discerning ruddy from brown.
Really, I did not notice the yellow in the SEB until the GRS rolled around and there were actually some "white" features along the SEB. Something to compare with the brilliance of the SEB hue helps to actually see the yellow as yellow instead of baseline for what might be white. And when those softer hues can be seen, really you have "resolved" more detail.
Anyway, thanks for indulging the discussion. Enjoying it.
"I identify on that band a clearly visible feature and place the others with reference to that one, rather than their actual position on the disk."
Yes, great technique. You almost have to do that. Sometimes I get lost, is that sketched festoon this one or that one? Arg!