Okay--I know this takes time but I like to give the depth of answers that I would in my office, tailored to the person so the best care results.
Black tongue spots or whole tongue turning black can be an inherited pigment situation or it can be from overgrowth of bacteria or fungus on the tongue (black hairy tongue). Smoking/tobacco use alone can cause it.
Brushing the tongue regularly does help overgrowth go away. It does nothing for hereditary pigmentation.
It is rare but it does happen that black spots on the tongue, especially raised black spots, is caused by mouth cancer. This is especially true in tobacco users or smokers of marijuana or other drugs (very unlikely that you do so from what you said above) as it's not only tar/other substances but heat that is implicated.
Therefore, I recommend that you get this checked out.
Now occasionally, what people think are black spots of the tongue, especially beneath the tongue, are actually blue--they are dilated veins (blood vessels) on the floor of the tongue. These are more prominent as you get older.
Regardless, I think that you should get these spots checked out. If there are other questions, please ask.
All the best to you!