Don't worry, they look fine. The leaves will yellow and drop towards the end of flowering because the plant is dying, cannabis is an annual plant meaning it completes its life cycle within one year.
What strain is the plant that's 7 weeks into flowering? And when you say 7 weeks do you mean that you switched the lights to 12/12 7 weeks ago, or do you mean you first noticed flowers 7 weeks ago? If it's an indica dominant strain then it should be ready to harvest after 8 to 9 weeks of flowering. If it's sativa dominant it will take a couple more weeks.