Warning: Prepare for ranting, dear readers. Nothing annoys me more than this. Nothing.
"It's" versus "Its."
Let's hit them one by one. The apostrophe only shows up after an "it" when you are making a contraction of "it" and "is." Sometimes "has" can pinch hit for "is."
Thus --
"It is a wonderful day," can be contracted to "It's a wonderful day."
"It has been somewhat fun," can become "It's been somewhat fun."
Now, if the "it" works as a pronoun, and you need to make it possessive, add the "s" but don't add the apostrophe. This seems to violate what some folks dimly remember from school, I know. But this is a special case.
Please. It doesn't need the apostrophe to be possessive.
"The house's paint peeled from the sun," should therefore be "Its paint peeled from the sun."
"The sweater's colors ran in the wash," should switch to "Its colors ran in the wash."
I know, I know. It looks a little funky. But resist that apostrophe. Take it out only for contractions. You will show people who know and love the language that you know and love it too. And you can dismiss my bitter mumbles.