Used multiple lines for better readability:
if ($sort == 'year' ||
$sort == 'make' ||
$sort == 'model' ||
$sort == 'color' ) {}
You may want to consider a switch statement
switch ($sort ) {
case 'year':
case 'make':
case 'model':
case 'color':
echo "it was one of those";
break;
default:
echo "it was not";
}