"glClearColor(0.6f,0.6f,0.6f,0.0f);
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);"
These 2 lines should be what you need to clear the screen.
I don't know what your codes are, so I can't tell much about it.
Are you sure you are running the above 2 lines before the second render function?
And, did you try glClearColor(0.6, 0.6, 0.6, 1.0);?