I love to wear white, but this summer I have already thrown away 2 cotton tops because the armpits went yellow after just 6ish wears. It's been like this all my adult life. I don't wear coloured tops at all due to excessive perspiration (Driclor works but I save that for one-offs, as it's pretty aggressive stuff), so in the summer my choices are black or white. Black lasts a bit longer, but it doesn't take long for my tops to get bleach-type stains under the arms and for the armpits to smell a bit, even straight after washing.
I've tried various washing techniques, but wonder what others do? I'm beginning to think that I have particularly toxic armpits...