Black hairball, White cat

Please help! :-(
I have a 10 year old Flame Point Siamese that is white/very light tan. I took him to the Vet 3 times within a month because he would vomit ALMOST daily, immediately after he ate. After bloodwork and every test known to man, we had nothing. My Vet finally said he was pretty sure Cody had a hairball he couldn't get up and may need surgery. I woke up the next morning and found literally, the biggest hairball I've ever seen. At first I thought my Pit Bull had "the runs" and left me a cow-sized patty to clean. Upon further investigation, including dissecting, I found it was 100% hair. However, all the hair was black. I do have black cats, but I assure you Cody doesn't groom them. Plus, I've had Cody less than 2 months. He prefers to keep distance between himself & the others.
He's yet to puke since this massive hairball was up chucked. With 5 cats, I don't want to email my vet this question, as I am always sending him stuff :-(
Is it possible for a white cat to have a black hairball?

Since he is a cream colored cat, there is no place for him to get a black hairball other than from other cats, the dog, or a toy he chewed up that had black fur on it.  I guess the only way cream colored hair could turn black is if it was dyed, i.e. perhaps bile could turn the hair black in his intestine.  Defiinitely put the hairball in a bag and put it in the freezer and take to the vet the next time you go.  I'm really glad that he was able to get it up and stop vomiting!

My calico's hairballs always look black when she upchucks them .  One reason is because they're extremely WET  , and I guess they probably ARE mixed with some bile or something deep inside her.  Now, granted, she DOES have some black fur, but not much.  But, I too have a couple of black cats, and I suspect that while grooming herself, she may also pick up some of  their fur from wherever she's laying, since they lay there too, when she's not there. 

Let's just hope it WAS Cody's, and the vomit's issue is now resolved

Thanks for the response guys! I found out through my vet that that hairballs that have sat in their stomach for a lengthy duration, typically turn black. This is caused my everything else that goes into their stomach and sits there, all while dissolving/soaking-up stuff around it.
Unfortunately, I've come to learn that Cody has chronic hairball blockage lol

Give Cody hairball remedy once or twice a day for a couple of days and then about once or week or more often if there are signs of hairballs. Intestinal hairballs can kill cats. Sometimes cats need enemas for hairballs and that can kill a cat, too.