This email was quite long, so I've edited out the unimportant or redundant parts. I'll also insert my comments as we go.
your color theory articles really inspired me and in the end were responsible for me finally starting to paint again. As usual, its Marines. I thought about a color scheme and painted a test mini. The main color i chose was hawk turquoise. As metal colors i chose both a bronze/gold and steel (no nmm, although chars/sergeants are gonna be done with a sky-earth effect). Being in the "neutral" spectrum, bone colors will also be used on a few details. So far so good.
I also wanted to use a white/light grey on parts of the armor, as i like the effect. The eyes were done in... well some kind of red/orange. This might change though, depending on ur input. (note that the shoulder guards arent done yet, this has a lot to do with my color problem described next)
Your model's eyes are a slightly orange red. Probably Blood Red. Your armor is Turquoise, or as I call it in my articles, "Cyan". It lies at the bottom of my color wheel, directly opposite red. This means that your eyes are painted in a complementary color to your armor. Which is why they're so striking and stand out.
I wouldn't change them a bit, unless you don't want the eyes to be striking.
My biggest problem is: the mini seems... incomplete. There is something missing, some details painted in a color that draws attention to the detail to make the mini more interesting. I looked at the color wheel u always post, but im not even sure where exactly my main color is. Somewhere between green and blue. I might glaze the armor with a super thin coat of watered down green to pull it towards the green spectrum a tiny bit.
(Rest of email skipped)
I've charted all of the standard Citadel colors to a proper hue wheel. You can see it here on the Color Theory Archive Page. Or just click the link below the site banner.
Your main color, as I said earlier, is Cyan. Which doesn't appear on traditional artist color wheels of the sort that you'll find in textbooks. You're also using Red for the eyes, and an orange for the bronze bits on the model. This means that you're using a bent split-complementary triad. Charted out, this is your scheme:
Now usually, I'd like to see that triangle of analogous colors at the top be perfectly perpendicular to the line of contrasting color at the bottom. But in your case I have a better idea. Let's go with a double-split complement instead. Like so:
So now we need to introduce a slightly cyan-ish blue into your model. Like so:
It's a subtle difference, but I've added some blue to the base and "white" bits on your model. This contrasts well with the bronze and unifies the colors. As a last step, I'd make any unit markings or other appropriate details the same hue as the model's eyes. Though you can go darker so it's less saturated and more subtle.
Oh, and one more thing... DRILL OUT THAT BOLTER SOLDIER!!!
That is all. ;)