Slightly warm off-white, not as warm as what we call ivory. They are about 1/16" thick and the holes are 1.5mm. Most are a bit iridescent, at least on one side. (Clearly these are not plastic buttons!)  Satiny, thick for their tiny size, durable, smooth and a bit shiny. None are grayish; that's a lighting/camera issue with the iridescence.  Most of the backs are the same; some may have a spot of seashell peach tone.   You'll get at least 95 buttons, for $7.25.  

They're between 10.5 and 11mm, just shy of 7/16" and definitely larger than 3/8".