hi deano1 been a while since i done some tig welding,hope the following is off some benefit not sure off the colours but the following info was given to me when i was on my welding course @ college
carbon/stainless steel thin sheet or plate d.c electrode negative preferred they recommend argon gas with thoriated tungsten pointed tip
carbon/stainless steel thin sheet or plate a.c with h.f possible on thin sheet they recommend argon(argon+helium)for deep penetration with zirconiated tungsten rounded tip
titanium all thicknesses d.c electrode argon gas thoriated tungsten pointed tip
nickel monel inconel all thicknesses d.c electrode negative argon gas thoriated tungsten pointed tip
copper and alloys sheets and plates d.c electrode negative preferred argon (or argon+helium)nitrogen also possible thoriated tungsten pointed tip
copper and alloys very thin material only a.c with h.f or s.i. possible argon gas thoriated or zirconiated tungsten rounded tip
aluminium and magnesium thick material a.c. with h.f. or s.i. preferred argon (or argon+helium)for deep penetration zirconiated tungsten with rounded tip
aluminium and magnesium thin material d.c. electrode argon gas thoriated or zirconiated tungsten with rounded tip
key:- d.c. direct current a.c. alternating current h.f. high frequency s.i surge injection.
like i say not sure off the colours but hope it helps
Red is Thoriated which should be good for DC, Zirconiated is white and suitable for AC, Ceriated is Grey and good for both AC and DC. There's Lanthanated as well which I think is fine for both but I can't remember what colour it is as I've never used them!