What color would a red book be in red light?

This is hard to find out knowing the information given. I'll contact my good friend detective Sherlock Homes (not Holmes, copyright issues). He has a lot of experience in solving mysteries. He once solved the case of how big is the ten foot tower. It took him a while, but he found out it was ten feet tall. I don't know how he did, but he did. Just contact me and I'll help you with your problem. I'm sure my friend Mr. Homes will be glad to help, worth a small fee of 10 dollars (plus 500 dollars tax and fees). Good luck and I'm here to help.