The ten Heavenly Stems (天干) form a cycle used with Earthly Branches to name years, months, days, and hours in the Chinese sexagenary calendar.
Each stem carries yin or yang polarity and an element flavor (Wood, Fire, Earth, Metal, Water). That is how you get a Water Dragon year vs a Wood Dragon year.
Element colors
Popular Chinese zodiac apps often show an element color on your birth year. That comes from the stem portion of the year pillar.