I don't know what you mean about "when everything is highlighted, nothing is"—shouldn't they be highlighted different colors, often diametrically opposed colors?

With my coloring most of the time I don't even notice the semantic coloring except when I'm looking for it, especially when I type a long variable or method name and I'm thinking "did I spell this right?", if I see the same name somewhere else and if it has the same color, then I have high confidence I didn't make any typos.