Conversation so far:
Who has Kim Jae-joong collaborated with?
Kim Jae-joong collaborated with label-mates The Grace for the Japanese version of their song Just for One Day“.
Has Kim Jae-joong had any other collaborations besides with label-mates The Grace for the Japanese version of their song Just for One Day“?
On 30 September 2009, Kim Jae-joong and bandmate Park Yoo-chun released a self-composed single Colors (Melody and Harmony)/Shelter.“

Question: Did he work a lot with Yoochun?
Self-contained rewrite: Did Kim Jae-joong work a lot with Yoochun?