Brief answer: Spondyloarthrosis and artery stenosis. Detailed answer : Hello,i ve read your health concerns and im gonna let you know that the coause of your shoulder pian may be related to a condition called spondyloarthrosis, which means that the surfaces between your neck vertebras are damaged, which can cause pain radiated through your shoulders. i advise you to do an XRay of the cervical vertebrae. About your other concern,different coloration of both arms, this sign suggest that there might be a stenosis of your arm artery, there is low blood flaw circulation. I would suggest to perform an echo color doppler of your upper limbs or an Angio CT Scan which is more detailed. I hope it helps with your health concerns. Feel free to ask again. Best Regards!