Maybe you can use <MarkFollowing bold = "true" italic = "false" color = "MidnightBlue">class</MarkFollowing> (though so far MarkFollowing was only used for single chars, e.g. \ in TeX-mode). MarkFollowing marks exactly the following word. For example in C#, MarkPrevious is used to make method calls bold.
Alternatively, you can take a normal Span and give the start token a different color. Example: the C# XML documentation span which has a gray beginning, but green line after that:
<Span name = "DocLineComment" ... color = "Green" stopateol = "true">
<Begin bold = "false" italic = "false" color = "Gray">///@!/@</Begin>
</Span>