Well just create a CSS Rule for this and embed the words in a span. To be honest i don't know what you mean with "every time in sigil", once you did it and saved it is persistent. Or do you mean you have always the same words to be colored?
Code:
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title></title>
<link href="../Styles/Style0001.css" type="text/css" rel="stylesheet"/>
</head>
<body>
<p>test <span class="red">test</span> test</p>
</body>
</html>
with stylesheet STYLE0001.CSS
Code:
.red {
color: #ff0000;
}