> Be aware that those 3 color screens are very slow to update, 15-20 seconds.

I just did a project with one. You are right, the three (or more) colour screens do indeed have very slow update cycles, and they usually don't support partial refresh either (just updating part of the screen)

BUT there are some tricks you can do. You can start most of them in two-colour mode, which does support partial updates, and you can define and upload a custom set of waveforms that govern how the screen performs its refresh and update cycles. I wrote an email to the company I purchased from (good-display) and they were very responsive and sent me some waveforms to try. These allow a much faster update (~1s) at the cost of some slight greyness, which gets worse over time, needing a full refresh after a while.

The resulting code I wrote now does something like -

  - start device (colour)
  - draw background in colour (15 seconds)
  - every minute, restart device (B/W) and draw 'active' areas (1 second)
  - every 15 minutes redraw background (full screen update, 15s)
  - every 24 hours run a screen refresh routine(1 minute plus)

It's not ideal, but it does allow you to do something like a static background image in color, then a clock and a few gauges that update more frequently.

(my screen refresh routine cycles each pixel through each of the colour transitions, black->white, black->red, white->red, and the reverse)

Yeah. They take a while, but as long as your project is only dealing with static images/data, you can update it at inconspicuous times. I recall seeing a calendar project that used a display like this. The red was used to highlight important things, and it only has to updated when something changes.

The full-color (7 or 8 colors to mix) take forever to update, but if you’re just displaying a photograph, update it at 2am and no one knows the difference.