suffusion font colors

Sounds like you’ll need to tamper with CSS.
When modifying themes at all, you should create a Child Theme or if you want to specifically change CSS, try activating a Custom Style/CSS plugin.

Have you either?

should i get to know how to make a child theme or activate the CSS plugin?

Yes or you’ll create extra work when your theme updates. All changes to theme files will erase on update.

If you haven’t access to the directory of your website, try using a Child Theme plugin, such as http://wordpress.org/extend/plugins/one-click-child-theme/ .

First may you post a valid link to your web page relevant?

Can you also provide the hexadecimal value of the darker colour?

To change the font colour on the navigation bar to a darker brown, add this CSS in your Child Theme stylesheet;

#nav a, #nav a:visited {
 color: #925f2c;
}

you have to go in your theme & and edit the font color in style.css template. Search /*#nav a, #nav a:visited*/ in style.css template & color edit:

#nav a,
#nav a:visited {
padding: 8px 8px 5px 8px;
text-decoration: none;
display: inline-block;
color: #925f2c !important; <– change here
}

For Suffusion you don’t have to go through creating a child theme for things such as these. To change navigation bar colours you can go to Appearance → Suffusion Options → Skinning → Navigation Bar Below Header.

Also, for creating a child theme for Suffusion you can get a starter child theme here: http://aquoid.com/news/2012/02/suffu-scion-a-starter-child-theme-for-suffusion/