You could use the HTML5 Tag <mark>:
<p>Enter the competition by
<mark class="red">January 30, 2011</mark> and you could win up to $$$$ — including amazing
<mark class="blue">summer</mark> trips!</p>
And use this in the CSS:
p {
font-size:14px;
color:#538b01;
font-weight:bold;
font-style:italic;
}
mark.red {
color:#ff0000;
background: none;
}
mark.blue {
color:#0000A0;
background: none;
}
The tag <mark> has a default background color...at least in Chrome.