Ignore the point, the majority of the points are along the trend line.
        
                    
             
        
        
        
Answer : Hypothesis.
Explanation : Hypothesis is defined as the supposition or proposed explanation which can be made on the basis of limited available evidence as a starting point for further investigation. Here, in this question the proposed explanation for the changing colors of the sky is an example of a hypothesis. 
A hypothesis has to be supported with scientific experiments which are reproducible by several experiments and test results have to be valid to be called as a scientific theory.