I'm gettign confused here, first I thought it was just going to be some form of table fill in color, but when you say "Focusing cursor in field" I think it's more an input field you want to change color in. For this you can use CSS, this example might give you an idear.
Code:
<html>
<head>
<style TYPE='text/css'>
<!--
INPUT {font-family: verdana, arial, helvetica,sans-serif;font-size: 8pt;}
.red{
background-color:#FF0000;
color: #FFFFFF;
}
.white{
background-color:#FFFFFF;
color: #000000;
}
// -->
</style>
</head>
<body>
<form>
Red style: <input type='text' class='red'><br>
White style: <input type='text' class='white'>
</form>
</body>
</html>