The Welsh singer refuses to take to the stage with his legs clad in any other colour as he is so worried his perspiration might be highlighted.
He explained: "I perspire a lot on stage, so the pants have to be black, otherwise the sweat will show through. When I started out, I'd wear really tight pants. Everyone wore tight pants, but maybe not quite as tight as mine."
Tom's penchant for skin-tight legwear once led to an embarrassing moment on stage, when his leather trousers burst a seam in front of hundreds of people.
He told Britain's Observer Woman magazine: "Once I was singing Kiss at a TV special in Cardiff and I came to the part where I do a squat, and these leather pants I was wearing split up the back. So I said, 'This is for people who don't believe I wear underwear,' and bent over so they could see the red briefs I had on. I've stopped that move now."