colors.java

public List<String> getCommonColors(String blueprintId, List<String> printProviders) throws IOException {
    List<String> commonColors = new ArrayList<String>();

    for (String printProvider : printProviders) {
        VariantsResponse variantsResponse = getVariants(blueprintId, printProvider);
        List<Variant> variants = variantsResponse.getVariants();
        for (Variant variant : variants) {
            Options options = variant.getOptions();
            String color = options.getColor();
            if (!commonColors.contains(color)) {
                boolean isCommonInAllProviders = true;
                for (String otherProvider : printProviders) {
                    if (!otherProvider.equals(printProvider)) {
                        VariantsResponse otherVariantsResponse = getVariants(blueprintId, otherProvider);
                        List<Variant> otherVariants = otherVariantsResponse.getVariants();
                        boolean found = false;
                        for (Variant otherVariant : otherVariants) {
                            Options otherOptions = otherVariant.getOptions();
                            if (otherOptions.getColor().equals(color)) {
                                found = true;
                                break;
                            }
                        }
                        if (!found) {
                            isCommonInAllProviders = false;
                            break;
                        }
                    }
                }
                if (isCommonInAllProviders) {
                    commonColors.add(color);
                }
            }
        }
    }

    return commonColors;
}