[ApolloScripter]

Hello cipi89 why are you formatting the hex-dec color code?, as it says on the Wiki, it must to be a integer or hex in RGBA, the way you are using, makes the parameter a String, so it gives the error. Just remove the format stuff and put on top of your GameMode:

pawn Code:

#define ColorName FF000080

So you just need to use:

pawn Code:

GangZoneFlashForPlayer(playerid, gangwars_Zone, ColorName);

The last two digits (80) is for the Alpha channel transparency of the GangZone.
For more information: https://sampwiki.blast.hk/wiki/GangZoneFlashForPlayer