Greg is wearing a gold shirt while speaking to Carol on the sofa. He leaves her to talk to Mike in the den, and now he's wearing a blue shirt. The next day as Greg arrives home from school; his jacket opens slightly, revealing a white shirt. He walks into the family room now wearing the exact same outfit as when he spoke to Mike the day before, the blue shirt. He walks into the kitchen wearing the gold shirt from the day before. This indicates that scenes were filmed out of sequence, and the script continuity person didn't do their job.
When Marcia asks Alice to help her with her "friend's" problem regarding snitching on Greg about smoking, she's wearing a jumper dress with a flowered blouse. Presumably, upon Alice's advice, she sought out her parents to tell them. In the next scene, when she's with her parents in the den, she's wearing a peach coloured blouse with pants. Not likely she'd have reason to change her clothes.
When Greg is sitting with Carol on the sofa after Mrs Johnson left, he's wearing a yellow plaid shirt. In the very next scene, when he's in the den with Mike, he's now wearing a blue plaid shirt. Again, no reason why he'd change his shirt.
When Greg is playing the guitar, Carol chides Mike by telling him "Talent is inherited" While Carol is by this time accepted as the boys' mother, it's doubtful Greg could have inherited any talent from her.