Take the opposite approach for a surprising take on words. Use white space and design around it for maximum appeal. This could be used with any color scheme and might be fun to do a time lapse of someone drawing around the words being advertised.
This would be a great poster to hang in a classroom as part of walls that teach! Prepositions are something that may be a little abstract for students to understand, but this is a great visual representation of what they are. This could work both on visual representation and skill within language arts. Students could then make up their own poster for another type of word, such as a verb.