* What's the primary color? Red for destructive and green for confirmation is given, but what about everything else?

* Given the primary color, how do I select the hue, saturation, and brightness to mesh with my existing color scheme?

* How do I pick the text color? Should it be lighter or darker than the background?

* What color will the button be when it's held down or disabled?

* If the button is particularly important, how do I give it extra weight? Otherwise, how do I ensure it has the same intensity as other buttons in its category?

* Maybe the button can be toggled. What color should I make its toggle state? How do I keep it legible while making it clear that it's not just a weirdly colored button?

* What color should the border be, if any?

...over and over again! Matters are further complicated by the fact that the user can pick their own hue for several prominent UI elements. There's also a dark mode, which multiplies the design effort by 2. (You can't just darken the existing colors and call it a day: many pairs of colors have to be switched in order to preserve the legibility, e.g. the color of a button background and its label.) Picking colors has become an incredible burden, forcing me to try colors over and over again until I find something that intuitively feels right. I've tried some algorithmic approaches ("if toggled, darken by 20%"), but it doesn't give consistent results. Perhaps switching to a perceptual color space (HCL?) would help, but it would be a major refactor. In the meantime, I have to make do with what I have.

(Sample screenshot: http://i.imgur.com/SRh5pPA.png)

Is there a good, systematic way to pick and organize colors for a theme, especially with modifiers? (Toggled, disabled, etc.)