Part of creating web design involves working with shades of color. At times, using a color for a HTML link may look good indeed, but the same Hex color code may not necessarily work as a background color. As a designer, you may have to work with different shades of the same color.
This article, the code side of color, explains the science behind hexadecimal code, but if you need to figure out colors quickly on your website, Colllor is a great resource that I have been using for several years. Check it out.