I've had glimpses, longer and shorter, in trance. My first one is among my profile posts, doesn't take a lot of scrolling.
The first glimpses took about 3 months of working on trance, and a few more than that of doing our daily meditations and improving in these. For the most part, I could see it with my eyes closed, quite different from visualizing something, simply observing what is already there.
It is colorful, generally fluid, and I've only ever seen it when filling it with white-gold light, so that's the only color I've seen, although the kind of rainbow shine it had is definitely there, and hard to compare with most things.
I'm sure it's different on higher levels, as seeing auras acts just like most other spiritual abilities: a gradient and not a simple on/off speech. You don't suddenly have the ability fully mastered, it progresses over time, probably to no end in sight.