The colors are from the South Vietnam flag and are set in deliberate vertical pattern, and have also been used on a horizontal position as well (like the tattoo on my arm). Let me give you a quick history. The Vietnam War became very unpopular in the USA in the late 1960s. Unfortunately, American citizens took their anger and put it on us Veterans. People spit on us, movies always portrayed Vietnam Veterans as drug/alcohol abusers, lazy, no good bums, baby killers, etc. They did us very wrong for a long time. That attitude started to change in the early 1980's to where it now popular to be a Veteran. People fly flags again and treat our present day servicemen and women with the respect they deserve. It's been an uphill battle, but Vietnam Veterans have been able to change the whole country's attitude towards Veterans.
We wear our "colors" with pride and try to make it easier for fellow Vietnam Veterans to recognize each other.