Those preview images look to me like it may be due to the color. You might be seeing dithering to make the background be a little dark.
Can you add color references to the @ ... SAY line which will override the color. Use COLOR RGB(0,0,0,255,255,255) I believe (been many years), but regardless it should be black on white, possibly COLOR "n/w+" (been many years :-)).
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I know.... crazy to be thinking of this stuff in 2020, right?
I'll give that a shot, with the assumption that the ":" on the printed output is the best representation the old dot matrix printer can do of grey. This would be a work-around, but hey, if it works I'll take it!
Thanks, Rick.