The feature code colours file (fcmap.txt) or colour table file associates feature symbolization codes in the ih_master.txt file with colour tokens in ih_colour.xml.
You can add or change the colour assignments directly by editing the file.
The format is <feature code><space><colour token>.
The file uses the * character as a wildcard. This means that if there is a feature code with NP* Nautical_Purple, all feature codes that start with NP will be displayed with the Nautical_Purple colour token.
The * Black entry sets black as the default colour for any feature codes not listed in the file.