The "line" is not what to look for. That is not even an identifying trait of what a Pastel is. A pastel is yellow/orange in color. Even a low quality baby can't be mistaken as anything other than a low quality pastel. Fire's are a bit tricky because a low quality one can look like a normal to the untrained eye. But distinguishing a Pastel from a Fire is very easy. Continue to look up pictures and you'll learn the difference.
PASTEL:
http://www.worldofballpythons.com/morphs/pastel/
FIRE:
http://www.worldofballpythons.com/morphs/fire/
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