IOS假设将一个十六进制的color转换成UIColor，非常有用

(UIColor *)RGBColorFromHexString:(NSString *)color alpha:(float)alpha { //color的值相似#fffeee,alpha的值相似1.0为透明度
int nums[6] = {0};
for (int i = 1; i < [color length]; i++) {
int temp = [color characterAtIndex:i];
if (temp >= '0' && temp <= '9') {
nums[i-1] = [color characterAtIndex:i] - '0';
}else if(temp >= 'A' && temp <= 'F') {
nums[i-1] = [color characterAtIndex:i] - 'A' + 10;
}else if(temp >= 'a' && temp <= 'f') {
nums[i-1] = [color characterAtIndex:i] - 'a' + 10;
}else {
return [UIColor whiteColor];
}

}
float rValue = (nums[0] * 16 + nums[1]) / 255.0f;
float gValue = (nums[2] *16 + nums[3]) / 255.0f;
float bValue = (nums[4] *16 + nums[5]) / 255.0f;
UIColor *rgbColor = [UIColor colorWithRed:rValue green:gValue blue:bValue alpha:alpha];
return rgbColor;
}