I have one thats a couple years old who was rehomed to me, he was pale before I had him and hes pale now. I helped take care of him for 2 years with no change to his color before he came to be fully in my care. I'm starting to think hes just old, kinda like hes going grey in the stripes i guess. Hes been in my tank which is glass all the way around for about 2-3 months now and hes still pale before he was in a tank you could only view from the top down. And hes in my tank with a goby and a melanaris wrasse, so I know no ones picking on him. He eats algae, nori, mysis, spirulina, everything thats offered. He was a little skinny when I first started caring for him but now hes borderlining overweight if anything. I think sailfins both lose color with age and for camouflage reasons too.