Without using the richmemo itself... you can also just change the RTF content.
If you look at the RTF source of the resulting output file, you'll something like
{\rtf1\ansi
{\colortbl;\red255\green255\blue255;}
\cf1 This is white text.
}
You can just change the colors in the \colortbl to reflect a darker color.
(the white one will be the 255,255,255 color)
Change it to 0,0,0 - For example {\colortbl ;\red0\green0\blue0;} for black.
There is no need to change the complete RTF.
When loading back in your program... you might want to change it back to white.