When you are using color for your website, you need to understand that while your screen might show the background as light green, another monitor can interpret it as grey and it all depends on the setting that the monitor uses. Some monitors are on 24-bit and while your monitor shows color palette #dddddd as light grey, an 8-bit might interpret it as goblin green. This is because #dddddd is not a browser safe color. Now, if you want your page to look the same every time for any monitor, consider using browser safe colors, there are actually a number of them.
Now, when you’re building web pages that uses colors, it is very easy to setup a color scheme which clashes, making it difficult for readers to view for a longer time. By understanding color theory, you can understand how color can be more effectively used for your website. We all know that the primary colors are red, yellow and blue. Orange, green and purple are secondary colors and many other variants can be made when all these are combined. How do you combine all these so that your site will not burn the eyes of your readers? You will then need to learn about color harmony.