Hey +seeds,
in the project it would just be adding a color to be inserted to the dyeable items.
In Legacy it is a bit more complicated, you would have to add an additional item for every piece of cloth you would want to have colored grey. That is, for example, add a new item to /tmwa-server-data/client-data/items/equip-torso, something like item[id]_GreyCottonShirt.xml, then add this to /tmwa-server-data/client-data/items/equip-torso/item_db_chest.txt and, for dying, add the dye and recipe to Rauk and add something to Selim. I cannot help much with this as I am not into Legacy code very much. To realize this you would have to dig coding system and make sure you change all relevant files.
Sorry this is not of much help

Yours,
- Mick