It can also be maroon, very dark brown, etc. This is because your period is different from, say, falling down and cutting your knee. That's 'new' blood. Your period isn't brand new.
Your period may also appear to be a light colour if it's not as heavy. It can be helpful to keep track of your period over the months - when you have it, what days are heavy, etc. This can help you know what's normal for your body and help alert you if anything changes.
If you've been getting your period for a long time and it's always the same - except for this time - then you should see a doctor. Otherwise, you should be fine. This is assuming that you haven't done anything that could cause you any problems (meaning unprotected sex, etc).
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