This error is seen at the start of a scenario run and does not prevent the scenario continuing. It is caused by the lack of a file called REAL_TIME_COLOURS.DEF in the GPS$USER (SYS$LOGIN) directory.
To resolve the problem you need to create the file. To do this select Data Text Colour from the Options menu of the Real Time Control Screen. This will initialise the colour control window. Just click OK or select a colour if you want to change from the default and a new file will be created. The scenario can continue to run while you are doing this.