Thank you for your query at DoctorSpring.com
The hypopigmented line that you are talking about at the junction of the penis and the body is normally present. Moreover penis is normally darker at its end towards the body. So both your suspicions and problems seem to be resolved.
Secondly the penis is darker in shade when it is shriveled and lighter when it is erect. Now this shriveled penis depends on the state of mind. Unless you have problem in erection while you are having sex, you need not bother a lot. The state and the size of penis varies over time depending on the state of mind and the temperature as well. So you need not bother alot.
Hope this clarifies,
If you have any further need for clarifications, do let me know.
Dr. Srikanth Reddy MD