Look at the colour

 

Look at the colour

A healthy tongue should: Be pinkish in colour
A dark red shade: Indicates inflammation
A brownish or black discolouration of the tongue is caused due of excess consumption of tobacco, gutka and paan.
A strawberry pink tongue could indicate the onset of scarlet fever or Kawasaki disease
A thick white coating could be due to the oversecretion of bile in the liver and gall bladder.
When the tongue turns blue or purple, it's time to seek urgent medical help.
White patches can indicate a fungal infection or leukoplakia.

Look at the surface
A healthy person's tongue must be light pink and moist.
Lack of normal texture called as bald tongue can occur due to deficiency of Vitamin B complex or Iron.
Patches or spots means the person could be prone to allergies.
A dry tongue is a sign of stress, since the salivary glands are not functioning at optimum level.