Soulmate AU is when one gets close to their soulmate, or makes a romantic action with them, the others favorite color appears as a heart on one's wrist. The color changes to their preference.

Shiro's heart color: Dark Purple
Keith's heart color: Bright Red
Pidge-Katie's heart color: Lime Green
Lance's heart color: Electric Blue
Hunk's heart color: Yellow
Allura's heart color: Magenta
Skylar's heart color: Dark Royal Blue

You may write (OC)'s favorite color down in the comments, so it appears on (Crush)'s skin once the two got close, or made a romantic interaction. YOU MAY ROLEPLAAAAAAAAY