Discolored ceramic tumbling media

I wouldn't worry about it. Did the tumbled stones look okay after completing the stage with the ceramic media? If so your ceramic media is okay. The black specs are probably flaking off a new tumbler bowl which is common. Did you get the black specs floating on top of the slurry when you finished the stage?

I run my ceramics through every stage, it doesn't bother them one bit...

If I recall correctly, what you are describing indicates you may have abrasive ceramics.  I don't have the specs on them, but I would only reserve those for a coarse grind, especially if you don't know the size of the grit that's embedded in them.

Where did you get the ceramics?  

While I can't say for sure, I don't know if those are abrasive or not, as I've never used or purchased the material. Most ceramic abrasives are used in metal finishing/deburring, but since you bought your stuff from lapidary suppliers, I would actually be surprised if those were abrasive.  Perhaps an email or phone call to your vendors might alleviate your concern(s).

Just for grins, I did a search and came up with this page where abrasives are sold.  In the photo gallery below the main photo, there is a photo of some abrasive cylinders.  While similar in appearance, they don't quite look the same as yours, as the flecks in theirs appears to be more prevalent, IMHO.

Perhaps jamesp can offer an opinion.

I did not realize you went that far with the ceramics you have.  I thought you'd only done 60/90 with the stuff.  Considering your results, and the fact the media does not look the same as the abrasive laden material, keep on rolling.

I received some well used, small triangle ceramic media as part of a bulk purchase. The ceramics had black particles in them. SEller told me that the black flecks were in the media when they were new.
I separated the used and new ceramics. Now have stage specific.
Some now have a high polish.

I do not use them for every tumble, only some.

I have tried to understand the effects of using harder media and softer media fernwood. This is the best I could figure:

I ran into a minor issue running ceramics when doing AO 220 and AO polish in the vibe with glass.
I ran many loads of glass. They were all consistent, 3 days AO 220 and 18 hours AO 14,000 polish out of the rotary. Like 60 loads all using Mohs 7 quartz pea gravel.
If I used Rock Shed Mohs 9 ceramics it consistently took 5 days AO 220 and 3 days AO 14,000.

I think I know why.
The only real difference is that ceramics are Mohs 9 and the pea gravel is Mohs 7.
I suggest using the same media for a given batch be it ceramic or quartz start to finish during 220-500-1000-polish(or what ever steps are used to get to polish).
So that the media shares the same finish as the target rocks for each step.

An example of why the media should be run with each step:
If fresh un-tumbled ceramic media is added straight out of the box to a batch ready for polish the rough ceramics will sure scratch your pre-polish to shreds. That's a fact.
Had the ceramic media been pre-polished it would help to polish the batch.

So if you use hard media it will likely take longer to reach a 220-500-1000-polish surface finish.
Softer media attains a 220-500-1000-polish surface finish quicker.
The hard media is likely slowing down each step it is used.
Especially when the hopper is full of soft material like glass.

There is another issue. Glass is not hard enough to break down aluminum oxide quickly, if it can at all.
So a percentage of(some type of) harder media must be added to assist breaking down the aluminum oxide.
How hard ? In my experience Mohs 7 media is plenty hard enough but it is quick to assume the finish needed for each step.

Assume you had ceramic media made of fused 220 grit diamonds. (This same situation arises with Mohs 7 or Mohs 9 media.)
It would stay with a 220 finish probably no matter how long you used it to tumble with because the diamonds are way too hard for Mohs 7 rocks to dull them.(with exception)
It's only use would be to grind a 220 finish on your rocks.(with exception)
The exception - if the diamond media was run *together long enough it should smooth each other(only diamond can cut diamond) eventually which brings up another unknown.
Ceramic media running with ceramic media will speed the finish on ceramic media because it is very hard.
The higher percentage of ceramic media used in a batch will help speed the abrasion(smoothing) of the ceramic media.
But you are using up more space in you hopper if you add more media. Best to use as little media as needed to get the job done.

All this is theory but I tried both on many repetitive loads of glass and the Mohs 7 media outperformed the Mohs 9 ceramic media by a long shot.
The media needs to be matched for the hardness of the rocks and the abrasives being used.
And I tried 10%, 20%, 30%, 40%, 50% media - what is the minimum amount needed ? I needed to know, I had much glass to polish.
One of the most used Lot-O recipes asks for 50% ceramic media for obsidian just saying. And a long schedule with several steps.
I need to try 25% quartz media in this Lot-O recipe. I think you will improve the speed and would be able to reduce the steps.
Guessing softer media and softer abrasive is used when tumble polishing Mohs 4 fluorite. I see tumble polished fluorite, our overseas neighbors do it all the time.

Yes, like Zirconium is Mohs 8. Not sure about tin oxide.
The most common is aluminum oxide so based tests on it.
I was not aware of a Mohs 5 ceramic though. Do you know what it is made of ? It may be a porcelain media.

Their is a lot of information about applications involving ceramic media types on metals and even plastics.
Using them on rocks(and glass) is a different issue.
Not much information from the manufacturers about that application.
The only knowledge I could glean was from the tests on glass and obsidian.