Though I don't know for certain if this will help, there is a way to reduce the maximum frequency with which the game's display will update every second. That would reduce the frequency of the blinking quite a bit, though it would also make the game look more like a slideshow proportionately to how low a number is used.
In the init.txt file under Dwarf Fortress's \data\init folder, there is a section that should look like this, as copy-pasted from my copy's file:
Change this to YES if you want to see an FPS counter at the top left.
[FPS:YES]
Use this to set the maximum frame rate during play. The movies are always capped at 100. A frame in this case is not graphical but related to the movement speed of a creature. A healthy, unencumbered dwarven peasant takes one step every 10 frames.
You may set FPS_CAP to 0 to make it uncapped.
[FPS_CAP:100]
Use this to set the maximum graphical frame refresh rate during play.
[G_FPS_CAP:50]
There are two forms of "FPS" here. The first, [FPS_CAP:100], is actually not the important one, because it caps the maximum speed at which the game will advance time by one step (there are 1200 steps in each dwarven day). The second one, [G_FPS_CAP:50], is the maximum Frames Per Second value that the game's display will update at, regardless of how fast the game time is being calculated.
Changing [G_FPS_CAP:50] to [G_FPS_CAP:1] will cause the game's display to update once every second, though creatures will move faster "behind" that speed (fast ones will appear to jump multiple tiles once per second). One frame per second is very slow, and may be slower than necessary to help your friend, if this does help.
If you use the above method, then you should also change [INTRO:YES] to [INTRO:NO] in the same file, because the intro movie's display speed can't be changed.
Another, more extreme (and possibly less effective), idea would be to change the colors DF uses in the \data\init colors.txt file so that there's less color variation. If I remember correctly, Dwarf Fortress uses only sixteen colors to fill in every ASCII character using the default rendering mode. (Graphics sets may use more colors and are not fully affected by colors.txt.) Changing all of the non-[BLACK:*:*] colors to a uniform shade of light gray would completely eliminate all color changes from any color that isn't black to any color that isn't black. Icons would still change as normal, but their colors wouldn't.
That would remove lots of visual information about objects on screen, but a bit of memorizing and checking with the loo
[k],
[q]uery and
[v]iew commands could make up for that. There would be a few other issues, such as not being able to tell when one menu option was selected. To counter that, evenly spaced shades of gray could be assigned to each color in DF (or only four shades, or eight...). That would be a compromise between the full color and black and white options.
colors.txt changed to have only black and light gray:
These are the display colors in RGB. The game is actually displaying extended ASCII characters in OpenGL, so you can modify the colors.
[BLACK_R:24]
[BLACK_G:24]
[BLACK_B:24]
[BLUE_R:192]
[BLUE_G:192]
[BLUE_B:192]
[GREEN_R:192]
[GREEN_G:192]
[GREEN_B:192]
[CYAN_R:192]
[CYAN_G:192]
[CYAN_B:192]
[RED_R:192]
[RED_G:192]
[RED_B:192]
[MAGENTA_R:192]
[MAGENTA_G:192]
[MAGENTA_B:192]
[BROWN_R:192]
[BROWN_G:192]
[BROWN_B:192]
[LGRAY_R:192]
[LGRAY_G:192]
[LGRAY_B:192]
[DGRAY_R:192]
[DGRAY_G:192]
[DGRAY_B:192]
[LBLUE_R:192]
[LBLUE_G:192]
[LBLUE_B:192]
[LGREEN_R:192]
[LGREEN_G:192]
[LGREEN_B:192]
[LCYAN_R:192]
[LCYAN_G:192]
[LCYAN_B:192]
[LRED_R:192]
[LRED_G:192]
[LRED_B:192]
[LMAGENTA_R:192]
[LMAGENTA_G:192]
[LMAGENTA_B:192]
[YELLOW_R:192]
[YELLOW_G:192]
[YELLOW_B:192]
[WHITE_R:192]
[WHITE_G:192]
[WHITE_B:192]
colors.txt changed to have black, light gray (for all non-grayscale colors), dark gray and white, to help with menu navigation:
These are the display colors in RGB. The game is actually displaying extended ASCII characters in OpenGL, so you can modify the colors.
[BLACK_R:24]
[BLACK_G:24]
[BLACK_B:24]
[BLUE_R:192]
[BLUE_G:192]
[BLUE_B:192]
[GREEN_R:192]
[GREEN_G:192]
[GREEN_B:192]
[CYAN_R:192]
[CYAN_G:192]
[CYAN_B:192]
[RED_R:192]
[RED_G:192]
[RED_B:192]
[MAGENTA_R:192]
[MAGENTA_G:192]
[MAGENTA_B:192]
[BROWN_R:192]
[BROWN_G:192]
[BROWN_B:192]
[LGRAY_R:192]
[LGRAY_G:192]
[LGRAY_B:192]
[DGRAY_R:128]
[DGRAY_G:128]
[DGRAY_B:128]
[LBLUE_R:192]
[LBLUE_G:192]
[LBLUE_B:192]
[LGREEN_R:192]
[LGREEN_G:192]
[LGREEN_B:192]
[LCYAN_R:192]
[LCYAN_G:192]
[LCYAN_B:192]
[LRED_R:192]
[LRED_G:192]
[LRED_B:192]
[LMAGENTA_R:192]
[LMAGENTA_G:192]
[LMAGENTA_B:192]
[YELLOW_R:192]
[YELLOW_G:192]
[YELLOW_B:192]
[WHITE_R:255]
[WHITE_G:255]
[WHITE_B:255]
I hope some of this information may be of use.