And please don't get me started on my rant about the Rainbow Demonstration. More people get maimed by it than literally any other chemistry demonstration. If you have access to a gas supply and a Bunsen burner, that's all you really need to see even subtle flame colors: the Bunsen flame is hot and mostly colorless, Bunsen invented it just for this exact purpose. I like to use wooden craft sticks which have been soaked in a couple changes of distilled water, this removes most of the residual sodium. Pick up a tiny bit of sample on the damp stick, put it in the flame, and colors appear. The only real downside is that sometimes the students dump salts into the Bunsen burners. To avoid corrosion this activity always ends with the burners being disassembled and washed and dried.