ccboxslinger,
In the browser, you'll have to use either the operating system settings, or the browser settings (if any) to change the colors. For example, in Firefox, you can go to Tools > Settings; Content, Colors... and you can choose the colors to use and whether to override the system colors. In Windows, you can change the same things in Advanced Appearance Settings, but it will impact all apps, not just the browser. (Of course, the browser settings will impact all websites, not just LDS.org. The only way to avoid that is some sort of plug-in that will override settings for a specific website. For example, in Firefox, I use Stylish to customize some frequently-used website. But if you don't know CSS, that might be more frustrating than it's worth.)
These sorts of settings don't always work as well or look as nice as you might hope, but you could give it a try.
If you need specific help, please reply with the operating system you're using (with version number), and the browser (again, with version) you're using.
FWIW,
Liz