expression, godan verb (-ru)
people are influenced by their surroundings
Proverb meaning that one's character is shaped by the company one keeps; often used to warn about the influence of bad companions. The literal image is that vermilion dye will turn anything red.
朱に交われば赤くなるというから、友達は選んだほうがいい。
They say 'he who touches vermilion will turn red,' so you should choose your friends carefully.
Both are proverbs about the influence of companions, but 類は友を呼ぶ emphasizes that like attracts like, while 朱に交われば赤くなる focuses on how one's environment changes one's character.
A classical Japanese proverb derived from the image of vermilion dye (朱) staining whatever it touches. The exact origin is uncertain, but it reflects a common East Asian motif about environmental influence.