Forgot to add to the last post - I/KG26 ( Roman numeral) indicates I Gruppe, whereas 1/KG26 (Arabic numeral) indicates 1 Staffel.
I(One) Gruppe would consist of 1, 2 and 3 Staffel, II (Two) Gruppe would be 4, 5 and 6 Staffel, and so on.
The first two letters of the codes (in black) indicated the Geschwader.
The third (coloured) letter was the individual aircraft within the Staffel or Stab (colour of letter indicating the Staffel or Stab.)
The last (black) letter indicated the Gruppe.
Staffel colours were :-
1, 4 and 7 Staffel = White.
2, 5 and 8 Staffel = Red
3, 6 and 9 Staffel = Yellow.
Geschwader Stab = Blue.
Gruppe Stab = Green.
Dark letters such as red or blue were often (but not always) outlined in white.
Yellow letters were mainly outlined in black, but there were exceptions.
White letters were mainly plain, but have been noted with black outline in some cases.