Walkthrough
Go to the Goblin Village, which is located well north of Falador (look at the worldmap) and talk with the generals.Now you need to make dyes to colour the goblin armours. To make the dyes, bring the ingredients to Aggie, which can be found in Draynor Village. She will ask for a few gps too.
Yellow dye: You need 2 onions to make this dye. Onions can be found north of Rimmington or north-east of Lumbridge.
Red Dye: You need 3 redberries. Redberries can be bought in the cooking store in Port Sarim, or picked from the redberry bush south-west of Varrock near the mining spot.
Blue Dye: You need 2 woad leaves. Talk with Wyson the Gardener in the park in Falador. If you offer him 20 gp, he will give you 2 for generousity. Otherwise, you will need to pay 15 gp.
Here are the goblin mails you need.
Orange Goblin Mail: Use an orange dye on a normal mail. To make orange dye, use yellow dye with red dye.
Dark Blue Goblin Mail: It's a Blue Goblin Mail. Use a blue dye on a normal mail to make it.
Brown Goblin Mail: It's just the normal mail!
Now, go to the generals again and talk with them. They don't like the orange one. Talk with them again. The blue is too colourful. Talk with them again, and give them the brown. They seem to like it, and you will get a gold bar. Quest complete!