Welcome to the community, @joo_hyung_lee! :grinning_face_with_big_eyes: Record links do not currently support custom colors. The only option to get colors in links is to use colored emojis in the primary field.
There are a few requests already for adding color to link fields, so your best bet is to show your support in those threads (these may not be all, but they appeared at the top of my search):
Even if a thread is locked and you can’t add further comments (as is the case with the last of those threads), you can still give any of the posts in that thread a thumbs-up to show your support.