background color of a control (winapi)

Question 1

Source code using a static control:

LONG WINAPI WndProc(HWND, UINT, WPARAM,LPARAM);

HWND hWndStatic;

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{   HWND hwnd;
    MSG msg;
    WNDCLASS w;

    memset(&w,0,sizeof(WNDCLASS));
    w.style = CS_HREDRAW | CS_VREDRAW;
    w.lpfnWndProc = WndProc;
    w.hInstance = hInstance;
    w.hbrBackground = (HBRUSH)GetStockObject(LTGRAY_BRUSH);
    w.lpszClassName = L"My Class";
    w.hCursor = LoadCursor(NULL, IDC_ARROW); 
    RegisterClass(&w);

    hwnd = CreateWindow(L"My Class", L"My title", WS_OVERLAPPEDWINDOW, 300, 200, 800, 600, NULL, NULL, hInstance, NULL);
    hWndStatic = CreateWindowEx(0, L"Static", NULL, WS_CHILD| WS_VISIBLE |SS_LEFT, 10, 130, 200, 20, hwnd, NULL, hInstance, NULL);

    ShowWindow(hwnd,nCmdShow);
    UpdateWindow(hwnd);

    while(GetMessage(&msg,NULL,0,0))
    {   TranslateMessage(&msg);
        DispatchMessage(&msg);
    }
    return msg.wParam;
}

UINT_PTR uTimerId;
LOGBRUSH lbrBk;

LONG WINAPI WndProc(HWND hwnd, UINT Message, WPARAM wparam, LPARAM lparam)
{
    switch (Message)
    {   case WM_CREATE:
        {   LRESULT lRes = DefWindowProc(hwnd, Message, wparam, lparam);
            HBRUSH hbr = (HBRUSH) GetStockObject(LTGRAY_BRUSH);
            GetObject(hbr, sizeof(lbrBk), &lbrBk);
            uTimerId = SetTimer(hwnd, 123, 1000, NULL);
            return lRes;
        }

        case WM_CTLCOLORSTATIC:
            if ((HWND)lparam == hWndStatic)
            {   SetBkColor((HDC)wparam, lbrBk.lbColor);
                return (BOOL) GetStockObject(LTGRAY_BRUSH);
            }
            return FALSE;

        case WM_TIMER:
        {   TCHAR szTime[128];
            HDC hdc = GetDC(hwnd);
            _tstrtime_s(szTime, _countof(szTime));
            SetWindowText(hWndStatic, szTime);
            ReleaseDC(hwnd, hdc);
            break;
        }

        case WM_DESTROY: 
            KillTimer(hwnd, uTimerId);
            PostQuitMessage(0);
            break;
        default:
            return DefWindowProc(hwnd, Message, wparam, lparam);
    }
    return 0;
}

Question 2

Remove the handler for WM_PAINT and call your PaintProcedure() when the timer fires: sample code

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{   HWND hwnd;
    MSG msg;
    WNDCLASS w;

    memset(&w,0,sizeof(WNDCLASS));
    w.style = CS_HREDRAW | CS_VREDRAW;
    w.lpfnWndProc = WndProc;
    w.hInstance = hInstance;
    w.hbrBackground = (HBRUSH)GetStockObject(LTGRAY_BRUSH); // WHITE_BRUSH
    w.lpszClassName = L"My Class";
    w.hCursor = LoadCursor(NULL, IDC_ARROW);
    RegisterClass(&w);
    hwnd = CreateWindow(L"My Class", L"My title", WS_OVERLAPPEDWINDOW, 300, 200, 800, 600, NULL, NULL, hInstance, NULL);
    ShowWindow(hwnd,nCmdShow);
    UpdateWindow(hwnd);

    while(GetMessage(&msg,NULL,0,0))
    {   TranslateMessage(&msg);
        DispatchMessage(&msg);
    }
    return msg.wParam;
}

UINT_PTR uTimerId;
LOGBRUSH lbrBk;
LONG WINAPI WndProc(HWND hwnd, UINT Message, WPARAM wparam, LPARAM lparam)
{   switch (Message)
    {   case WM_CREATE:
        {   LRESULT lRes = DefWindowProc(hwnd, Message, wparam, lparam); // I don't have any controls in the main window
            HBRUSH hbr = (HBRUSH) GetStockObject(LTGRAY_BRUSH);
            GetObject(hbr, sizeof(lbrBk), &lbrBk); // for use in timer logic
            uTimerId = SetTimer(hwnd, 123, 1000, NULL);
            return lRes;
        }

        case WM_TIMER:
        {   TCHAR szTime[128];
            HDC hdc = GetDC(hwnd);
            _tstrtime_s(szTime, _countof(szTime));
            SetBkColor(hdc, lbrBk.lbColor);
            TextOut(hdc, 200, 200, szTime, _tcslen(szTime));
            ReleaseDC(hwnd, hdc);
            break;
        }

        case WM_DESTROY: 
            KillTimer(hwnd, uTimerId);
            PostQuitMessage(0);
            break;

        default:
            return DefWindowProc(hwnd, Message, wparam, lparam);
    }
    return 0;
}

Question 3

Oh, I was not using winapi since years, so I could forget how gdi works, but I don't understand how could I not get it, you was talking about: remove WM_PAINT - the whole handler, not only the calls I do from it.
Earlier I solved problem with histogram flickering. It is very fast procedure, all algorithms in camera class I wrote and checked in python, so I was sure it should work. And it works. I had to turn off code optimalization.
Your tip solves timer flickering problem and overall interface efficiency. But there is now not solved white background problem. Should I use subclassing to give my controls the color of my choice? I tried on WM_CREATE

hStatic = CreateWindowEx( 0, "STATIC", NULL, WS_CHILD| WS_VISIBLE |SS_LEFT, 10, 130, 200, 20, hwnd, NULL, hInst, NULL );
        SetBkColor(GetDC(hStatic), lbrBk.lbColor);
        SetWindowText( hStatic, buf );

but without an effect.
Here is my interface looks like now: https://www.dropbox.com/s/7123ef7wi1sars8/follower2.png
Thank you. :D