Not able to change Background

Not able to change Background
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I am very new with cocos2dx and also with c++ and I have started with the helloword sample game. I am trying to change the background,
But, I am also facing same issue.
In my project,
I have changed

class HelloWorld : public cocos2d::CCLayer
class HelloWorld : public cocos2d::CCLayerColor

& if ( !CCLayer::init())
if ( !CCLayerColor::initWithColor(ccc4(0, 0, 255, 255)))

but getting error as follows:
Invalid arguments ‘
Candidates are:
bool initWithColor(const cocos2d::_ccColor4B &, ?, ?)
bool initWithColor(const cocos2d::_ccColor4B &)

and also

The type ‘HelloWorld’ must implement the inherited pure virtual method ‘cocos2d::CCRGBAProtocol::setOpacity’

Please help me to solve this issue.