It was part of elementary school English.
“The sky is blue” is a fact statement. “The sky is green” is a fact statement. “The sky is striped red and purple with gold accents” is a fact statement. Each of these statements is either true or false.
“The Virgin Mary was assumed, body and soul, into Heaven” is a fact statement. It must be either true or false. We simply can’t prove the truth or falsehood of the statement with the available information. “The earth is billions of years old.” “The earth is thousands of years old.” Both are fact statement, although they can’t both be accurate.
“The red and purple sky is beautiful” is an opinion statement.
I see the light. :)