create
// Convenience methods for creating colors
+ (UIColor *)colorWithWhite:(CGFloat)white alpha:(CGFloat)alpha;
+ (UIColor *)colorWithHue:(CGFloat)hue saturation:(CGFloat)saturation brightness:(CGFloat)brightness alpha:(CGFloat)alpha;
+ (UIColor *)colorWithRed:(CGFloat)red green:(CGFloat)green blue:(CGFloat)blue alpha:(CGFloat)alpha;
+ (UIColor *)colorWithCGColor:(CGColorRef)cgColor;
+ (UIColor *)colorWithPatternImage:(UIImage *)image;
#if __has_include(<CoreImage/CoreImage.h>)
+ (UIColor *)colorWithCIColor:(CIColor *)ciColor NS_AVAILABLE_IOS(5_0);
#endif
解释：
支持gray colorspace支持HSB colorspace支持RGB colorspace支持Quartz color支持pattern image，tile模式填充，相位默认为0，即image top-left corner与填充区域原点对齐支持Core Image color
init
// Initializers for creating colors
- (UIColor *)initWithWhite:(CGFloat)white alpha:(CGFloat)alpha;
- (UIColor *)initWithHue:(CGFloat)hue saturation:(CGFloat)saturation brightness:(CGFloat)brightness alpha:(CGFloat)alpha;
- (UIColor *)initWithRed:(CGFloat)red green:(CGFloat)green blue:(CGFloat)blue alpha:(CGFloat)alpha;
- (UIColor *)initWithCGColor:(CGColorRef)cgColor;
- (UIColor *)initWithPatternImage:(UIImage*)image;
#if __has_include(<CoreImage/CoreImage.h>)
- (UIColor *)initWithCIColor:(CIColor *)ciColor NS_AVAILABLE_IOS(5_0);
#endif
注：各UIColor模式对应init
改变alpha
// Returns a color in the same color space as the receiver with the specified alpha component.
- (UIColor *)colorWithAlphaComponent:(CGFloat)alpha;
注：返回receiver相同UIColor，除alpha自定义
预定义颜色
// Some convenience methods to create colors. These colors will be as calibrated as possible.
// These colors are cached.
+ (UIColor *)blackColor; // 0.0 white
+ (UIColor *)darkGrayColor; // 0.333 white
+ (UIColor *)lightGrayColor; // 0.667 white
+ (UIColor *)whiteColor; // 1.0 white
+ (UIColor *)grayColor; // 0.5 white
+ (UIColor *)redColor; // 1.0, 0.0, 0.0 RGB
+ (UIColor *)greenColor; // 0.0, 1.0, 0.0 RGB
+ (UIColor *)blueColor; // 0.0, 0.0, 1.0 RGB
+ (UIColor *)cyanColor; // 0.0, 1.0, 1.0 RGB
+ (UIColor *)yellowColor; // 1.0, 1.0, 0.0 RGB
+ (UIColor *)magentaColor; // 1.0, 0.0, 1.0 RGB
+ (UIColor *)orangeColor; // 1.0, 0.5, 0.0 RGB
+ (UIColor *)purpleColor; // 0.5, 0.0, 0.5 RGB
+ (UIColor *)brownColor; // 0.6, 0.4, 0.2 RGB
+ (UIColor *)clearColor; // 0.0 white, 0.0 alpha
注：预定义颜色预先cached，并非调用时创建
系统颜色
// System colors
@interface UIColor (UIColorSystemColors)
+ (UIColor *)lightTextColor __TVOS_PROHIBITED; // for a dark background
+ (UIColor *)darkTextColor __TVOS_PROHIBITED; // for a light background
+ (UIColor *)groupTableViewBackgroundColor __TVOS_PROHIBITED;
+ (UIColor *)viewFlipsideBackgroundColor NS_DEPRECATED_IOS(2_0, 7_0) __TVOS_PROHIBITED;
+ (UIColor *)scrollViewTexturedBackgroundColor NS_DEPRECATED_IOS(3_2, 7_0) __TVOS_PROHIBITED;
+ (UIColor *)underPageBackgroundColor NS_DEPRECATED_IOS(5_0, 7_0) __TVOS_PROHIBITED;
@end
获取颜色信息
// Access the underlying CGColor or CIColor.
@property(nonatomic,readonly) CGColorRef CGColor;
- (CGColorRef)CGColor NS_RETURNS_INNER_POINTER CF_RETURNS_NOT_RETAINED;
#if __has_include(<CoreImage/CoreImage.h>)
@property(nonatomic,readonly) CIColor *CIColor NS_AVAILABLE_IOS(5_0);
#endif
// Convenience methods for getting components.
// If the receiver is of a compatible color space, any non-NULL parameters are populated and 'YES' is returned. Otherwise, the parameters are left unchanged and 'NO' is returned.
- (BOOL)getWhite:(nullable CGFloat *)white alpha:(nullable CGFloat *)alpha NS_AVAILABLE_IOS(5_0);
- (BOOL)getHue:(nullable CGFloat *)hue saturation:(nullable CGFloat *)saturation brightness:(nullable CGFloat *)brightness alpha:(nullable CGFloat *)alpha NS_AVAILABLE_IOS(5_0);
- (BOOL)getRed:(nullable CGFloat *)red green:(nullable CGFloat *)green blue:(nullable CGFloat *)blue alpha:(nullable CGFloat *)alpha NS_AVAILABLE_IOS(5_0);
解释：
如果receiver并非Core Image Color模式，获取Core Image Color模式属性throw exception获取gray color space，HSB color space， RGB color space属性时，如果receiver兼容，返回YES及对应属性值，如果receiver不兼容，返回NO
Drawing Operation
// Set the color: Sets the fill and stroke colors in the current drawing context. Should be implemented by subclassers.
- (void)set;
// Set the fill or stroke colors individually. These should be implemented by subclassers.
- (void)setFill;
- (void)setStroke;
解释：
set设置填充和轮廓颜色setFill设置填充颜色setStroke设置轮廓颜色
