Assuming your shirts are made from shirting rather than some infernal artifical mix or blend...
Shirting is a yarn dyed fabric, which means the yarns are dyed (and washed) before the fabric is woven. From that point it goes through several finishing processes before being shipped to a shirt maker who undoubtedly washes it before making your shirt. I can't speak for other shirt makers, but I also wash every shirt before sewing on the buttons. The chances of any colour (or color) leaching from your shirt into anything else you might be washing, is therefore zero. The thing to be careful of is colour from other garments leaching into your shirt. To avoid nasty surprises, if I must machine wash, I only ever wash shirts together, and as one other member recommends I also agree that washing in cold water is ample sufficiency and adds a "belt and braces" degree of safety to the proceedings.
Enjoy,
Shirting is a yarn dyed fabric, which means the yarns are dyed (and washed) before the fabric is woven. From that point it goes through several finishing processes before being shipped to a shirt maker who undoubtedly washes it before making your shirt. I can't speak for other shirt makers, but I also wash every shirt before sewing on the buttons. The chances of any colour (or color) leaching from your shirt into anything else you might be washing, is therefore zero. The thing to be careful of is colour from other garments leaching into your shirt. To avoid nasty surprises, if I must machine wash, I only ever wash shirts together, and as one other member recommends I also agree that washing in cold water is ample sufficiency and adds a "belt and braces" degree of safety to the proceedings.
Enjoy,
