Energy Levels Change the Color

When you heat an atom, some of its electrons are "excited* to higher energy levels.
When an electron drops from one level to a lower energy level, it emits a quantum of energy.
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The wavelength (colour) of the light depends on the difference in the two energy levels.
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We can see only those transitions that correspond to a visible wavelength.
In a hydrogen atom, for example, we can see only the transitions from higher levels to n = 2 .

As	Arsenic	Blue
B	Boron	Bright green
Ba	Barium	Pale/Yellow-green
Ca	Calcium	Orange-red
Cu (I)	Copper (I)	Blue
Cu (II)	Copper (II) non-halide	Green
Cu (II)	Copper (II) halide	Blue-green
Fe	Iron	Gold
In	Indium	Blue
K	Potassium	Light purple to red
Li	Lithium	Deep pink to dark red
Mg	Magnesium	Bright white
Mn (II)	Manganese (II)	Yellow-green
Mo	Molybdenum	Yellow-green
Na	Sodium	Bright yellow
P	Phosphorous	Pale blue-green
Pb	Lead	Blue
Rb	Rubidium	Red/Purple-red
Sb	Antimony	Pale green
Se	Selenium	Bright blue
Sr	Strontium	Crimson
Te	Tellurium	Pale green
Tl	Thallium	Bright green
Zn	Zinc	Blue-green to pale green