Do you mean within the neo4j browser? If in the browser, my first thought is through GRASS file configuration (color based on a tag/value), I don't believe that is possible yet. (has been requested)
I'm pretty sure this isn't what you want, but there is one way (sort of). You could add a new label to the nodes you want to highlight, using the browser settings to change the color for that label. The labels could be removed, and re-added with the next query. This is a bit of hack though, with a lot of caveats.