The diamond pattern is not Hapkido at all but related somehow to the Jido Kwan (TKD) organization.
I'm neither an Hapkido guy nor JDK, but I'm curious. Is there a connection between the two where some Hapkido folks would take on the JDK's top? So much so that a diamond pattern top is referred to as an "Hapkido uniform" in most MA uniform companies. My school in suburban Chicago (in the 80's) used to train with JDK folks & their master wore a diamond top. My sabum nim wore one as well, but he was Chung Do Kwan.