Verified answer

it is the cation, the positively charged ion.

when heated, the electrons in the atom become "excited" - they start jumping up to higher energy levels as they are provided with heat energy to do this. however, the electrons start falling back down in steps to lower energy levels, or back to their ground state (the shell they were originally in). when falling back down, energy is released, in the form of light, which is why you see the flame colour.

Li red

Na strong persistent orange

K lilac (pink)

Rb red (reddish-violet)

Cs blue? violet?

Ca orange-red

Sr red

Ba pale green

Cu blue-green (often with white flashes)

Pb greyish-white