Typically yes, when your body produces mucus it's almost transparent but becomes darker as it sits there. Various colors green to brown from bacteria doing stuff to it and in it. ..For me and from my experience, transparent, great! "fresh" thin mucus and the lungs are at ease, no reaction etc. Green, lungs are likely producing more mucus as a response to something but it's relatively infection free. Dark green, brown and strange colors are bad and bacteria or certain bad types of bacteria doing their thing and there's an infection. But this might be different from person to person so don't take that as a pointer.