This is not possible with pure CSS. However you can use lettering.js to get a ::last-word
selector. CSS-Tricks has an excelent article on this: CSS-Tricks: A call for nth-everything. You can then do the following:
h1 {
color: #f00;
}
/* EDIT: Needs lettering.js. Please read the complete post,
* before downvoting. Instead vote up. Thank you :)
*/
h1::last-word {
color: #00f;
}