"The purple car is fast."

Translation: 보라색인 자동차가 빠릅니다.

[SvedishPlumber]

How often do people use 자동차 instead if just 차?

[wintertriangles]

In my experience it's 50/50

[S0TY4]

보라색인 자동차 -> 보라색 자동차

[thaikanguy]

보란 자동차 should be accepted

[mhin1]

보란 is not a word.

보라 is a Sino-Korean word so it must be paired with 색 to be used as an adjective.