When you create online elements for your website or email, you may work with a tool that asks for your official colors in a specific format.
Colors online are designated in hex format, a pound sign followed by six characters. For example #000000 is black and #FFFFFF is white.
If you have loose brand guidelines and know what your colors generally are, like dark blue and olive green and need to find the closest standard color, then use this tool to find the most common web colors:
http://www.w3schools.com/tags/ref_colornames.asp
If you have very specific colors, but don't know the numbers that correspond for web design, this handy tool help you find the color designation:
http://www.w3schools.com/tags/ref_colorpicker.asp
Finally, you may have very specific details on your logo colors for print, but the codes are in Pantone or RGB format, but you need to know the hex color.
Here are a couple of online conversion tools:
http://www.javascripter.net/faq/rgbtohex.htm
Finding your brand colors is important, and something you should only need to do once. When you've identified the right codes, mark them down and you'll be set for future designs.