gistfile1.groovy

    def save() {

        request.withFormat {
            json {
                println "came here"
                render params?.colors?.myParam
            }

            html {
                render "html"
            }
        }
    }
    
    //test
    def "js test" () {

        given:
        request.contentType = "application/json"
        controller.request.content = "{colors: {myParam: 'a value', param2: 'value 2'}}"

        when:
        controller.save()

        then:
        controller.response.status == 200
        response.contentAsString == "a value"
    }
    
    //test output
    response.contentAsString == "a value"
     |        |               |
     |        null            false


    //However, when request is initiated with RESTConsole with same string put in the RAW body then the response is correct ('a value')