It is totally normal for your lawn to loose its lush green appearance this time of year. If you are in a northern zone, it is getting ready to go dormant. That is where the plant dies from the "Crown"( ground level) up, but the roots will remain active until the ground freezes. At that point the grass will go into full dormancy, until next spring.
If this is the case you can put down a winterizer type fertilizer.( use a broadcast spreader as opposed to a drop spreader) This will help your lawn by strengthening its roots, but not creating much more top growth.
Even if you are in a southern climate, with the lack of sunlight since the days are shorter, your lawn will not appear as richly colored. You can alter this by putting down a fertilizer that is high in nitrogen, and also has iron. But if you are in a area where the lawns go into dormancy, you will not want to do this, as it will be like giving a kid a bunch of sugar right before bed time.

Hope this helps.
Mike

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