Here is the problem. I use UIColor to some views and I used colour meter to compare colour in simulator with colour in an image, they are the same. This simulator is running on iMac.
Now I have another macbook air running same code, but the colour is different from that original image. And I can see it is different from the simulator on iMac.
EDIT:
DigitalColor Meter gave me the same value for both simulator, but the value for original image is different.