Not sure if you've solved the issue.
After a few attempts on my own, playing with regedit, I have solved the issue (had tried it for a few weeks earlier last year, given up for months, then accidentally solved it today).
SOLUTION:
win + r (or right click start, 'run')
run registry: 'regedit'
go to
HKEY_CURRENT_USER\Control Panel\Colors
Look for 'AppWorkspace'
if your default font color is gray, the data value is probably something like '157 157 157'
double click 'AppWorkspace' and change the data value to '0 0 0'
save
restart
and have your father read the text with ease