Addict, even those of us who are well-schooled in the world of grammar make that slip sometimes. I'm a summa cum laude English major and I actually did it in a published article recently (SO embarassing, and it was otherwise one of my best articles, too  ).
We're so programmed at a young age to use the apostrophe as a signal of possession that it's almost impossible to break for the its/it's exception.
My pet peeve, though it when people use improper pronoun/noun agreement ... e.g. "Every child must pick up their bag" or "the team won their fifth game." 
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1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)
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