Low-hanging fruit is the braindead R/G/B/Cyan/Magenta/Yellow used by some terminals in response to ANSI escape codes: https://sdkmvx.files.wordpress.com/2008/08/ansi-colors.png
In my mind, there's three types of colouring: None, Designed-By-Human, and the aforementioned Eye-Searing-255 (which should really be killed off or at least not be the default for anything used seriously). It's disgusting to open source code using vi or similar and have it presented in Eye-Searing-255.
Lol....this. If your primary workstation OS is Windows then I recommend grabbing a copy of MobaXTerm. It has the ability to override and tame the "Eye-Searing-255" beast with its own themes (Solarized Dark and Light, Pastels etc). No more "oh-my-god-my-eyes" when you open up "ooby-doofer.pl" in vim.
I do make exceptions. For example, I color my cursor, as well as highlight matching parens if the cursor is on one of the pair (changing just the foreground color of the paren, not inverting it). The only color I use is red.
I don't make any objective claims that this is better, my aim is to make something "done well and tasteful", as you say.
Judicious, typographically aware use of bold and italic or oblique in source highlighting can be a wonderful thing.
Personally I am working with a white background, so I try to keep the syntax colors all very dark, so while the different colors can be seen, they should not distract from reading. The correct amount of highlighting very much depends from the language at hand, but it can be very helpful in separating elements, just as an example take this function parameter list:
func foo(name, family string, age, size int) {
The correct reading of this parameter list entirely depends on the placement of the commas and the knowledge that "string" and "int" are parameter types - highlighting the type elements can help a lot.
With the availability of high-dpi displays, perhaps colors should be replaced with more traditional ways of markup as used in book-printing, replace coloring with different typesets and fonts.