Color indicators do in fact have rules meaning: on a card like Karoo Myr Cat, the lack of an indicator means it would need an extra ability to say that it's white.

Graveyard icons, on the other hand, are officially meaningless, and they aren't used with the modern card frame at all, even for reprints of cards that originally had the graveyard icon (the Commander version of Wonder, or the upcoming reprint of Ray of Revelation in Dark Ascension).

I'm not going to argue whether they should exist or not. I'm just wondering how useful people found them when they existed. I mean, the whole point was so that you could easily spot the gravestone symbol in your graveyard, when your cards were fanned, and, therefore, know that you had effects down there. Did that work with people? Did anyone scan for the graveyard symbol over looking at individual cards?

Back in the day, I did find them faintly useful. I was sad when Wizards said they wouldn't be happening on cards after Odyssey block.

What's strange is that they still use them on MTGO (for new cards), acknowledging that they are in fact useful.

I always found it to be an appealing little graphic icon too, though it doesn't quite mesh with the modern frame.

Hah, and mtgo doesn't need them; as it could easily fan out just the cards in graveyard that matter; and your opponent can't watch you looking.