Complex sentence: The girls have a choice of which colour crest they want on their jumpers: red or navy blue; the red makes the girls stick out like a sore thumb and the navy blue blends in so well that you can't even see it.
Split into simpler sentences: The girls have a choice of which colour crest they want on their jumpers: red or navy blue. The red makes the girls stick out like a sore thumb and the navy blue blends in so well that you can't even see it.