OK - here's a mini (less than all inclusive) primer.
Traditionally, the basic colors found in the flashes/SSI/DUI represent the following in our culture:
Blue - sky, freedom, intelligence
Green - life, balance, harmony, stability, nature, forest, plains and forests of Europe
Red - blood, warfare, sacrifice, power, valor
Yellow (Gold) - hope, positive, traditional, Asia
Black - night, mystery, covert
Grey - shadowy, in-between black and white, nebulous
White - purity, overt, openness
Additionally, in the military:
Teal Blue and Gold - colors of unassigned units (e.g., pre-Branch SF)
Purple - joint service command
Additinally, the black and gold Airborne tab was retained for its historical connection to the Airborne Command SSI originally worn by SF - there was a teal blue/gold Airborne tab for a short period but it was never fully embraced or authorized.
Now, for the following (just to mention a few flashes):
5th SFG RVN - originally all black, then the black w/white border 5th SFG + diagonal stripes denoting addition of personnel from 1st SFG (yellow) and 7th SFG (red) as well as an image of RVN national colors, then back to black w/white border.
SF Det Europe - traditional forest green (Europe) of 10th SFG + diagonal stripes of FRG national flag (black, red, gold).
46th SF Co/USASFT - black (covert nature of unit) w/gold border (1st SFG unit) + diagonal stripes of Thai national flag (red, white, blue, white, red).
1st SFG - yellow (Asia) + black border added to commemorate death of JFK.
SF not assigned to SF unit - jungle green (SF branch) with grey border and diagonal stripes indicating nature of assignment (white = overt, black = covert, purple = joint).
OK - now you can ponder the rest for yourself.
Richard's $.02
