To choose a thread color audition colors by unrolling a fair amount of thread over the different color areas of the quilt all at the same time. Stand back and take a look over the quilt. Does the thread accomplish your goal? Have you thought about the look you are going for? Does the quilt need "perking" up? Maybe you want a shiny thread or something that really shows up. Do you want the piecing to shine? Go with a thinner non-shiny thread. First time quilting? Maybe if you aren't confident of your skill you should go with a thread color that blends blends well. Is there a color you want to emphasize. Go with the thread matching it.
Keep auditioning threads until you find what works for YOU!! Not what great aunt Matilda would have done. Have fun and welcome to the quilting world..."warning - warning- this is addicting"