Do you mean the shadows? There are no terrain tag lights, only terrain tag shadows. If you want to change the shadow ambient color, it would be in map defaults.
For changing light colors however, you would want to either modify an existing light, or duplicate one within the custom light setting. In your given light's settings, you can change either the tint or the color filter to change the light color.
And if on the off chance you meant changing the numbers for the terrain tags, they're under the game settings. You can then change the tileset's terrain tags from there to the ones in game settings, in case you're using the tags for other purposes.