Well you can't rly edit the color_accent, because then it would change a lot of other things too. If you want different color in some specific color, example red, you have to edit the /usr/share/themes/red/meegotouch/libmeego-keyboard/style/libmeego-keyboard.css

It's immediately in the second line

MVirtualKeyboardStyle {
font-color: $FONT_COLOR_KEYBOARD;
}