* "Blue jean" is usually plural: We generally refer to multiple "jeans" as a pair of pants.
* Subject-verb agreement: The verb "is" should agree with the subject "blue jean" (or "jeans").
Here are some better ways to say it:
* "Your blue jeans are good." (This is the most common and grammatically correct way to say it.)
* "Your blue jean jacket is good." (If you are referring to a jacket.)
Let me know if you have any other sentences you'd like help with!