Nope, I'm throwing in the towel. I'm thinking I got what the yellow is, as in the sun, but no idea what the blue might be, unless it's one of the blue items in the store or the blue button on the vending machine, but my colorblindness might be ruining it for me. Followed the walkthrough to the letter, but I've no idea what it's specifically referring to by sins, except maybe the the sun, as I said, and what other people have said.
That aside, this was an enjoyable hour and half I spent, I just wish I could figure out what you're asking for to reach what I'm assuming would be classed as the "good ending." Like someone below said, though, it's weird that showing the bloody knife to Yua Nizu (I'm assuming, since that's the name in the walkthrough, that's who the mother is) in the online version has her commenting on it, but not in the premium version. Anyway, thank you for this game, I've just no idea what to do to get that last scene.