No matter how close I think I am to the symbol I'm supposed to use, the game basically tells me that I did it wrong and wasted color.

As long as you get the glyphs to produce their effect, I wouldn't worry about the voices saying you're wasting colour. Getting the hang of producing which one you want is more important. The voices aren't happy about you using colour one way or another, anyway.

Seconding the above response, unless the game throws up actual text telling you that you failed (it's been a while since I last played so I forget the exact text it gives) to draw the correct glyph then you shouldn't worry too much.

The game is actually pretty forgiving with most of them anyway, aside from the donor glyph but that fact is pretty well documented and acknowledged by the developers.