Katherine: Aye, you’ve hit the nail on the head — what’s “white” and what’s “black” can indeed change (witness Nephi slaying Laban, for example). And while it can be difficult to tell what the right or wrong is for a given situation, the point is that there is a right and wrong. Some things are sins across the board, to everyone; some are sins peculiar to the sinner. Susanna Wesley had some wise words on the matter:

“Take this rule: whatever weakens your reason, impairs the tenderness of your conscience, obscures your sense of God, or takes off your relish of spiritual things; in short, whatever increases the strength and authority of your body over your mind, that thing is sin to you, however innocent it may be in itself.”

As an example, I find that eating sweets (candy, cake, cookies, ice cream, etc.) obscures my sense of God and increases the strength and authority of my body over my mind. I certainly do not think that that’s the case for everyone, and I don’t judge all the sweet-eaters out there (most everyone, really ;)) to be sinners. Nor do I think it’s a particularly grievous sin for me either, but it remains something that separates me from God even just a little bit. And I have enough pulling me away from God as it is — I need all the strength I can muster to draw near to Him, so I don’t eat sweets.

Rikker: I think even the smallest sins are still repugnant to God, though we ourselves may minimalize their evilness. Can a God of utter honesty be anything less than disappointed by a white lie? He’s more than willing to forgive us so we can pick ourselves up (or let Him pick us up, rather) and move on, but that doesn’t mean He excuses the sin.

More directly in answer to your question, it seems that the “shades” with all the examples you listed have to do with the repentance side of the coin, not the sin side. Sin is sin, period. Black is black. Some sins are harder to repent of, but even the two-second-repentance sins are still an abomination in the sight of God. It has to be that way, I think — if it weren’t, God would cease to be God.

What truly matters, I believe (though I’m still learning this myself, I’ll admit), is that we become like God in that we find even the smallest sins a stain on our heavenly natures. We can’t lose hope, of course, and that’s what the Atonement is for, but we’ve got to get to the point where we lose all desire to sin, where we view sin the same way God does. And what I find myself doing instead is rationalizing the little sins, telling myself that since God will forgive them, they’re not that bad. I do it because I don’t like feeling icky inside. But is that the right thing to do? (I’m not saying you do this, by the way. It just seems to be the result of focusing too much on the apparent gradations of sin.) What God wants us to do, I think, is to accept that sin feels nasty, and then cling wholeheartedly to the Atonement so we can get rid of the darkness and become children of light.

The main focus then becomes Christ and the Atonement, which is as it should be. All sin is bad, regardless of how we humans rank it, and regardless of how easy or hard it is to receive forgiveness. The Lord cannot look upon sin with the least degree of allowance. And because sin is so horrible, we need Christ all the more. He’s the only way.

There are unforgiveable sins, sins which are forgiveable but for which one can be excommunicated, sins which require counsel from priesthood authority, sins which are everyday and are regularly forgiven through personal repentance…

Maybe call it shades of black.

For example, when my oldest brother was a kid, he decided one day that he wanted to stay home from church. Rather than making him go or leaving him behind, my mother stayed home with him. My brother has never missed church since that day. I don’t doubt that my mother listened to the Spirit and that her decision was “white.” That’s the key, though–that she listened to the Spirit and made a decision. There were other decisions my mother could have made that would also have been “white.” For example, she could have gone to church with the rest of the family and left my brother at home. I think that would also have been a “white.” For another parent, insisting that their child go to church might be a “white.” For a parent who perhaps struggles with church attendance, staying home with their child from church might be a “black.” Much of it depends on motivations, I think.

Perhaps this is what many people mean by “gray areas” after all–not that there isn’t right and wrong, but it can be difficult to tell in any given circumstance what is right and what is wrong. The only thing we know for certain is that following the Spirit is “white” and not following the Spirit is “black.” The application of that principle varies widely, though there are certain “white” trends, such as the ten commandments, that should be followed unless the Spirit prompts otherwise (as in the case of Nephi killing Laban).

I do agree, though, that it’s refreshing to hear someone declare boldly that there are absolute truths–that there is right and wrong. Believe me, having grown up in the Northern California public school system, where moral relativism prevails, and where I was constantly hesitant to express my opinions about things for fear of seeming “intolerant,” “bigoted,” or “close-minded” (choose your liberal buzz-word), I feel quite giddy when I hear quotes such as the C.S. Lewis one you referenced here.