When students rehearse, help them to recite their lines accurately and not leave out any details. Sometimes a particular twist of wording is essential. Embellishments must be added with caution. Students can add them, but only after they can analyze them to be sure the changes don't alter whether people are Brights or Braves. Have students perform parts of the play for one another so that they can discuss and analyze them together.
Students can then try out the assumptions one at a time.
Sometimes it is useful to make a chart or table of the possibilities. It make take quite a few days for the students to catch on to ways to find out who the Brights and Braves are. Give them time, and try to assist them in structuring their thinking if they become frustrated. It's not uncommon for students to lose solutions as fast as they find them. Help students to make tables, write down statements or use other tricks to remember how they figured something out.