The best parameter is the light - I am with Ocelaris in post #3. People will argue with this, but true full-spectrum lights with spectrum from 350 to 850 are the best - this means fluorescent tubes and metal halides. As long as I use one of these lights, I can have great success with a wide range of swings and parameters.
Growth:
Higher levels of N and P will inhibit calcification. This is well documented and really indisputable. There are levels that will still grow coral plenty well and still be able to measure. The rule of thumb for me is that if the coralline is not spreading and creating new "spots" on the glass, then it is a bit too high for optimum calcification. You can maintain and get corals to grow a bit with P at .1 and N at 25, but this is probably too high for optimum growth - you will see tanks at these levels, but if you dig in enough, you will find that all of the periods of fast growth were not at these levels (people are not usually dynamic enough to see the difference in now and then).
For color:
This totally depends on your goals. Lower levels of N and P will have different colors than higher levels. When you have too high of levels, every color will have a tint of green in them. Really high levels and nearly everything will be green and brown. The Euros and people who really like them some ULNS systems really like the contrast and electric colors that super low nutrients will bring (lower than seawater - hence the U for Ultra) - these people will be at .001P and .01N or about 10x lower than seawater. Some folks like the rich, saturated colors that slightly higher nutrients will bring - somewhere in the .2P and 2-5N (about 20x more than seawater) is a good place to be here, but .4 up to 10 is also common. In the end, the color that you like is up to you - none is better or worse.
For me, my tank keeps it's self at about .01P and .1N and the color and growth are both outstanding - this is pretty close to seawater. This is more LNS, not ULNS - if you are not artificially driving the N and P low, then it cannot be Ultra. I would not keep them this low if I was dosing organic carbon, or GFO since I would be scared that they would get too low and I would aim for probably .02-.04P and 1.0 N... but I don't have to worry about this.
Coming back around to lights. I have noticed anecdotally in small/moderate numbers that people who tend to stay with lower nutrients are also feeding the coral with higher-quality lights. I have not seen too many Zeo tanks with LEDs, but plenty with fluorescent and metal halide. I really think that this matters and if you are into LEDs, then you need to keep your nutrients up of else you could be a small swing away from RTN or STN whereas a different tank could handle that small swing without any problems.
I don't think that the levels alk, calcium, magnesium and strontium are all that important as long as they are in balance with the alk between 7 and 11 - I keep the alk at 10.5 in my frag tank and the frags look and grow just like the ones in my display at 7.5. However, if you are driving N and P low with chemicals and media, then you MUST have your alk around 7 to inhibit calcification or else the coral will calcify faster than the tissue can grow and your tips will burn... and then the other elements in balance to the 7 alk. The only thing that I like to offer on elements is that complete addition in balance will really help - CaRx is best for this since it adds alk, calcium, mag, strontium, potassium and a few others in balance, but you can do this with all kinds of methods.
I have all kinds of methods to have a tank handle the N and P at sustainably low-but more-than-enough levels - I can post more about this if you want, but I have already typed enough.
Those two things are not mutually exclusive.
