How do I create NSColor instances that exactly match those in a Photoshop UI mockup?

Question

My UI designer gives me great UI mockups created in Photoshop. I want to exactly match the colors in the mockup, but every time I create a color using the -colorWithCalibratedRed:green:blue:alpha: method of NSColor, the colors do not match.

I have tried sampling the colors from the Photoshop mockup using the Pixie app in /Developer/Applications/Graphics Tools/ and it copies an NSColor definition to the clipboard, but these colors are not correct when I build and run the app.

If I use the values that the Photoshop color picker provides, they are not correct either.

I suspect this must be something to do with the fact that I'm sampling a calibrated color from the screen and so the values are incorrect, but I am not sure how to work around this.

If I use -colorWithDeviceRed:green:blue:alpha: and pass through the values it looks correct, but then the color is not consistent on other systems.

Is there a way to do this reliably?

Answer 1

There's no such thing as a "pure" RGB color that's consistent from one display to the next. Unless you're working in a standardized color space, the numbers that show up for a color on one display will probably render slightly differently on another.

Have your designer convert your mock-ups to a standard color space such as sRGB. Then you can use the methods on NSColor that take not just component values but the color space the components are in; this will get you colors that should look similar on any display.

In other words, a color swatch made from (R, G, B) = (1.0, 1.0, 1.0) in Photoshop using sRGB should look virtually identical to a color swatch drawn using a color you get this way:

NSColorSpace *sRGB = [NSColorSpace sRGBColorSpace];

CGFloat components[3] = { 1.0, 1.0, 1.0 };
NSColor *sRGBRed = [NSColor colorWithColorSpace:sRGB components:&components count:3];

Note though that +[NSColorSpace sRGBColorSpace] is only available on Mac OS X 10.5 Leopard and above. If you still need to run on Tiger, you could write a little utility app that runs on 10.5 and converts the canonical sRGB colors to the calibrated RGB space:

NSColor *calibratedColor = [sRGBRed colorUsingColorSpaceName:NSCalibratedRGBColorSpace];

Regardless of whether you use sRGB or the calibrated space, once you have a set of colors, you could put them in an NSColorList that you write to a file and then load from your application's resources at runtime.