Locate the file profile.xml at \Program Files\Ubisoft\Ghost Recon Advanced Warfighter\Settings\profiles\graw_profile_default

and open it with a text editor (like Notepad).

under <settings>, you will see a list of options, locate the line :

<classic_crosshair value="false" />

and change it to

<classic_crosshair value="true" />

Now locate the line

<ret_color value="29 137 151" />

and change the numeric values, where the 3 numbers represent the Red, Green and Blue values respectively. If the line does not already exist, you can add it.

You can use the following guide for selecting other colours.

Red <ret_color value="255 0 0" />
Black <ret_color value="0 0 0" />
White <ret_color value="255 255 255" />
Green <ret_color value="0 255 0" />
Cyan <ret_color value="0 255 255" />
Blue <ret_color value="51 51 255" />
Orange <ret_color value="255 165 0" />
Yellow <ret_color value="255 255 0" />