Lilac and potassium flames

 

Mrs B's lilac bush is in full bloom and reminded me that the official description of the colour of potassium in a flame test is lilac.

I know that this is because electrons are excited and go up energy levels. When they de-excite, they emit photons and the wavelength depends on the set up of the electron levels in the atom. The colour tells us something about the electron energy levels in potassium atoms. I found this brilliant answer. I have missed telling my classes that it is a flame test to use the electrons available to turn the vaporised ions back into atoms so that the electrons in the atoms can then go up and down the levels. I'm also interested that there is deep red here that I cannot see.