From Fu Xuan's 《
太子少傅箴》 (Admonitions for the Crown Prince's Tutor), Western Jin dynasty:
故近朱者赤,
近墨者黑;
声和则响清,
形正则影直 — therefore those near cinnabar turn red, those near ink turn black; if the sound is harmonious the echo is clear, if the form is upright the shadow is straight.