I need to highlight an item in a toolbar with a color that is distinct from other colors that are already present.
This accent color will be used in any currently selected item, row, or other item of interest.
How can I compute, derive, or hack a color that is appropriate for such an audience ?
There are different types and degrees of color blindness. So, what one color blind person can't see, another may be able to see perfectly fine.
The absolute safest bet is black and white. But, the general rule of thumb is to use colors that are high contrast in terms of light and dark (ergo, black and white).
A color-blind person may or may not be able to see red or green. But, you can use red or green and be more mindful of color-blind people if you go with different degrees of lightness and darkness. So, even though someone might not be able to see red (for instance), they could still ascertain a difference between a pinkish color and a dark red. In my experience, highlighted menu items are typically done with a darker shade of whatever color the menu item already is rather than an entirely different color. This strategy should be fine.
Another good rule of thumb is to use symbols in addition to colors. For instance, if you're working with KPI indicators where green means good and red menas bad, you could also use a check and an X, or a smiley face and a frowny face, etc.
Here's a nifty article that might help: http://www.somersault1824.com/tips-for-designing-scientific-figures-for-color-blind-readers/
Use greys.
Also, most color blind people are red-green colorblind, and so am i. So i can give you some first hand knowledge here.
So, from my point of view, you should avoid similar brightnesses / saturation levels of red and green. As they are less distinct.
Edit: If you avoid a mix of red/green overall you are statistically safer.
