What is the condition of the sentence: "If the sky is blue, it is sunny"?
This sentence is a conditional statement: if the sky is blue, then it is sunny. This means that the sky must be seen to be blue for the sun to be visible.
The condition of the sentence "If the sky is blue, it is sunny" is that the sky must be visible and the sun must be visible (or type this sentence as "if the sky is visible and the sun is visible, then it is sunny").