It's because we also use sino-Korean words(=hanja-eo, 한자어) which were affected by Chinese, hanzi(汉字), and the sino-Korean make up more than 65% of Korean vocabularies. The sino-Korean are often used in written or formal situations.
For example,(as to "red color")
빨강 = native Korean word
적색(赤=red,色=color) = sino-Korean word
빨간(the base form is "빨갛다") + 색(色) = mixed^^/
\^o^/