颜色设置：

指定RGB，參数是：红、绿、黄、透明度，范围是0-1

+ (UIColor *)colorWithRed:(CGFloat)red green:(CGFloat)green blue:(CGFloat)blue alpha:(CGFloat)alpha;

指定HSB，參数是：色调（hue），饱和的（saturation），亮度（brightness）

+ (UIColor *)colorWithHue:(CGFloat)hue saturation:(CGFloat)saturation brightness:(CGFloat)brightness alpha:(CGFloat)alpha;

当前的颜色改变透明度后的颜色：

UIColor *color = [UIColor redColor];
UIColor *cl = [color colorWithAlphaComponent:0.5f];

自己定义255的颜色值，将255转成0-1

CGFloat R  = (CGFloat) 225/255.0;
CGFloat G = (CGFloat) 66/255.0;
CGFloat B = (CGFloat) 88/255.0;
CGFloat alpha = (CGFloat) 1.0;UIColor *myColorRGB = [ UIColor colorWithRed: R  green: G  blue: B  alpha: alpha  ];
self.tableView.backgroundColor = myColorRGB;

最后附上

UIColor官方API文档：

Creating a UIColor Object from Component Values

• + colorWithWhite:alpha:
• + colorWithHue:saturation:brightness:alpha:
• + colorWithRed:green:blue:alpha:
• + colorWithCGColor:
• + colorWithPatternImage:
• + colorWithCIColor:
• – colorWithAlphaComponent:

Initializing a UIColor Object

• – initWithWhite:alpha:
• – initWithHue:saturation:brightness:alpha:
• – initWithRed:green:blue:alpha:
• – initWithCGColor:
• – initWithPatternImage:
• – initWithCIColor:

Creating a UIColor with Preset Component Values

• + blackColor
• + darkGrayColor
• + lightGrayColor
• + whiteColor
• + grayColor
• + redColor
• + greenColor
• + blueColor
• + cyanColor
• + yellowColor
• + magentaColor
• + orangeColor
• + purpleColor
• + brownColor
• + clearColor