Just curious, do the different colors signify any different functionality? If not, does it really matter what color they are (I know, red is the "standard" color for dummy stuff)?
FWIW, the description of the item at the link you provided reads (at least now):
"Snap Caps allow safe dry firing while protecting firing pin, sear and trigger. Excellent for firearms safety and storage. Dry Fire Dummy Rounds are made of tough Red or Blue plastic exterior with solid brass base. Ideal for training, working firearm actions and dry firing."
Based on the current description, it appears they are giving the disclaimer that the customer cannot specify color and the choice is up to them.