Windows GUI change button color

See more:

C++

Windows

color

buttons

GUI

I wanna change button colors when the user click on it.
The main plan is: every month 10th one worker's button go to red and if the worker done his job then click on the button and it going to be green.
I have no idea what to do.
I already have this code... I just created a window and add a button to it:

#include <windows.h>

LRESULT CALLBACK WindowProcedure(HWND,UINT,WPARAM,LPARAM);

void AddButton(HWND hwnd);


LRESULT CALLBACK WindowProcedure(HWND hWnd, UINT msg, WPARAM wp,
	LPARAM lp)
{
	switch (msg) {
	case WM_DESTROY:
		PostQuitMessage(0);
		break;
	case WM_CREATE:
		AddButton(hWnd);
		break;
	default:
		return DefWindowProcW(hWnd, msg, wp, lp);
	}
}

void AddButton(HWND hWnd)
{
	CreateWindowW(L"Button", L"Change colors", WS_VISIBLE | WS_CHILD,
		350, 200,
		100, 100,
		hWnd,
		NULL,
		NULL,
		NULL);
}

What I have tried:

So I tried WM_LBUTTONDOWN... so i think this is something when the user click on the button the program will do something. i put in the switch(msg) case WM_LBUTTONDOWN:
but no idea what's next