Creating a NSColor with RGB value

Also don't forget to do the following conversion from the actual RGB values you get, lets say from Photoshop...

an RGB of (226, 226, 226) could be instantiated as a NSColor using the values:

Red:   226/255 = 0.886... 
Green: 226/255 = 0.886...
Blue:  226/255 = 0.886... 

[NSColor colorWithDeviceRed:0.886f green:0.886f blue:0.886f alpha:1.0f];

Why 255? 8-bit color channels range from 0 to 255 (inclusive). When normalized this is scaled to the range [0,1] (inclusive). See references for conversions from normalized values to unnormalized values and vice versa.

References

• OpenGL ES Full Specification, See Table 2.7 on Page 38
• Unreal Engine Color Conversion

float red = 0.5f;
float green = 0.2f;
float blue = 0.4f;
float alpha = 0.8f;

NSColor *rgb = [NSColor colorWithDeviceRed:red green:green blue:blue alpha:alpha];

Per the NSColor documentation:

NSColor *myColor = [NSColor colorWithCalibratedRed:redValue green:greenValue blue:blueValue alpha:1.0f];