Coming in late to the discussion, I would offer a couple of comments -
Taber is correct in that black is used for armor defeating rounds, from AP projectiles to the LAW rocket. Yoda is also correct. However, our color codes have changed several times over the years, and black paint with white markings was used during the 40s-50s for training/display munitions. I'm at work with a new computer and don't yet have Photoshop installed so pardon the quality of the photo, but here is a crop from a shelf picture including
three common training projos. Two of them are admittedly AP, but the third you can see is an M64 75mm WP. There are many more examples of this color combination used in this way, but that one is the closest to hand.
Second comment, in your first photo of this chain; 137742, there is a second projectile. Nothing too special, but I like to call attention to it because it appears to be another WWI German 17cm naval round. I forget the designation, but we have discussed previously. No one is completely sure why, but these are very common in Michigan, Indiana, Ohio - I have had as many as 5, I've seen 4 more in MI, and just recently saw two more in Oklahoma. Often misidentified, I've seen them often mistaken as 175mm, the last two were identified as US navy 6-inch. If my assessment of the photo is correct I'd be interested to know how yours was described?
Last point, be very cautious what you purchase from folks on some of the sites. Many of the people have no idea what they have or what hazards they may represent. They may, in good faith, pass to you something identified as safe which in fact may not be. Case in point, in your third picture (Army 3) in the lower right you have three 20mm fuzes (M55?) which have the appearance of live items with the det/booster still present. These may very well be inert, but not knowing your level of experience or training I would recommend caution, both from a safety and a legal perspective.

