Gray tux but what color vest?

I like the Herringbone Silver Vest or the Geometrics Silver Vest

I think they are the closest to the Calvin Klein Gray 2-Button Super 110s Satin Edge Peak if that is the tux you are doing.

go to the store and see if they can do a mock up for you. Or ask them which they say matches the best.

My brother had the same kind of colour for his wedding His tie was a soft pastel blue.

What are your wedding colours? Either go with a muted colour of your colour palette (ie, a soft watermelon, almost diluted) or use the vest to pull in other colours you may be using. Otherwise, choose a grey slightly lighter or darker than the jacket - this will give enough definition without giving too much contrast.

Just remember that the jacket will pick up the colours in the waistcoat that are closer to its own colour. My groom is wearing a dark charcoal jacket with a lighter grey waistcoat and black skinnies (and a navy blue tie). The jacket seems lighter when looked at by the waistcoat and darker with the jeans. The waistcoat also looks a bit darker with the jacket. Colour swatches give you a general idea of colours, but you will be amazed at how the colours pull themselves together when put into an ensemble!

My groom is wearing that same tux. He is wearing the turquoise tie and vest and so are his groomsmen, but with a different design in the fabric. Your groom could wear a white vest or gray vest like Haley suggested.