How To Support Custom Colors

Why can't I use custom colors?

In the native game, there is a class called BannerManager for managing the banner data. A method called GetColorId within is used for finding a color's ID by its hex value from a Dictionary called ColorPalette, which contains all the registered colors from all banner_icons.xml files loaded into the game.

The method is implemented something like this:

public int GetColorId(uint color)
{
    for(int i = 0; i < BannerManager.ColorPalette.Count - 1; i++){
        if(BannerManager.ColorPalette[i].Value.Color == color){
            return i;
        }
    }
    return -1;
}

As you can see, it treats ColorPalette like an array and iterates through by index, whereas it is actually a dictionary and should be accessed by its key , which is not necessarily a series of 0-based continous integers.

When you tries to import the custom banner colors of your mod, the color IDs will very likely not fit into the "valid" range of 0 to Count - 1. The code above will then throw an exception for retrieving a value from the dictionary with a bad key.

How to patch?

You'll need to patch it with Harmony. The following code snippet is an example of how to do it:

[HarmonyPatch(typeof(BannerManager), nameof(BannerManager.GetColorId))]
[HarmonyPriority(Priority.First)]
internal class FixGetColorId
{
    private static bool Prefix(ref int __result, uint color)
    {
        foreach (KeyValuePair<int, BannerColor> colorEntry in BannerManager.ColorPalette)
        {
            if (colorEntry.Value.Color == color)
            {
                __result = colorEntry.Key;
                break;
            }
        }
        __result = -1;
        return false;
    }
}