Welcome to HEALTHCARE MAGIC..
I have gone through your query and can understand your concerns..
As per your complain black to freakish coating on on tongue is due to a condition known as Black hairy tongue
and is caused due to improper cleaning of tongue leading to accumulation of debris and bacteria over the tongue that leads to dark stained tongue surface..
It can also occur due to long term intake of only soft meals, taking any medication that stains the tongue like Bepto-Bismol, reduced cyclic shedding of the tongue papillae that accumulates debris and bacteria, excess intake of tea and coffee..
Nothing to worry as it is harmless and not indicating a sign of any serious illness as you did not have any abnormality with investigations for your tenderness in spleen
I would suggest you to start cleaning your tongue with a tongue cleaner/ scraper/
Gargle with 1:1 solution of hydrogen peroxide
You can also chew hard foods as they clean tongue by friction.
Always gargle after eating anything.
Clean your tongue using a tongue cleaner..
Drink plenty of water..
If still does not improve within a month consult an Oral Physician and get evaluated..
Hope this information helps..
Thanks and regards.
Dr.Honey Nandwani Arora.