As far as the content of the technical documentation is concerned, testing one combination for each separate space heaters heat generator and housing is sufficient where only the color differentiates the housings.
Disclaimer: Please note that the European Commission cannot provide a legally binding interpretation of the EU legislation, as this is the sole competence of the European Court of Justice. Any remarks from the European Commission services are without prejudice to the position the Commission might take should related cases arise in a procedure before the Court of Justice.