You're 99% there. The leading characters need to be white, with the tailing characters being green.
- chunks should vertically move down together, they don't just change color
- leading char is a bright green with outer glow
- movement doesn't always start at the top
- there are gaps in the chars
- there are vertical groups as small as 1 char that change chars at random
- there is no trailing transition in the color
(did actually lol)
It might be a decade too late but better late than never.
[1] Wikipedia calls it the "Matrix digital rain", see https://en.wikipedia.org/wiki/Matrix_digital_rain.
- The "random" groups don't look random at all to me. More like there's a series of "standing" characters left behind by the light-green leader, and behind that there's a stream of "running" characters advancing at a different rate. We only see the running characters through gaps in the standing characters, and only in cells that the leader has already visited.
Sadly I never really used canvas before, so I don't know how to hide the dark-green afterglow.
Also: the afterglow is caused by the main loop filling the entire canvas with a black rect with very low opacity. The result is that after so many frames, everything but the actively drawing characters are much darker. Increase the opacity if you want to reduce the length of the effect.