What's the difference between plain and clear?

Question

Answer

Clear :

very obvious : not causing or allowing doubt

easily understood

free from doubt or confusion

Plain :

having no pattern or decoration

not having any added or extra things

Answer

Both plain and clear can mean the same thing, "easy to perceive or understand".

Plain can also mean "not decorated," "without additional options", "simple," or "ordinary."  
Plain is also a type of landscape, a large area with few trees, usually covered in grasses.

Clear can also mean "transparent" or "see-through".

Answer

Depends on the context, could you provide some more info?