You have two options.
1. Set the body tag to the specified blue color: <body style='background-color: #0000FF'> (Find the colors and their corresponding codes using a search engine. #0000FF is a bright blue)
2. Create an image 1 pixel by 1 pixel of the blue color you want to use. Set the body tag to display that image: <body style='background-image: url("myBlueImage.gif")'>
I have used the inline styles. You could do this using a linked sheet, or the <STYLE> tag in the header or your HTML.
1.
BODY
{
background-color: #0000FF;
background-image: url("myBlueImage.gif");
}