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How do the flame-test colors of lithium, sodium, potassium, rubidium, and cesium differ?

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A color-coded periodic table of the elements displays each element's symbol and atomic number, with categories such as alkali metals, noble gases, halogens, transition metals, and actinoid elements distinguished by different background colors. — alkali metal Modern version of the periodic table of the elements (printable).

The characteristic flame colors of the alkali metals serve as qualitative indicators for identifying these elements in aqueous solutions. When subjected to a flame, each of these elements imparts a distinct color:1

These colors result from the emission of light at characteristic spectral lines when the atoms are excited by the heat of a flame. While these observations are useful for qualitative identification, quantitative analysis is typically performed by measuring the intensity of these spectral lines using instruments such as an inductively coupled plasma (ICP) spectrometer. When testing for one alkali metal in the presence of others, interference can occur, which is often managed by using specially prepared standard solutions.1