Manejando el color de fondo de una ventana (WinApi)

#include <windows.h>
#include <stdio.h>

#define ID_BUTTON 1
#define ID_EDIT_1 2
#define ID_EDIT_2 3
#define ID_EDIT_3 4

/*  Declare Windows procedure  */
LRESULT CALLBACK WindowProcedure (HWND, UINT, WPARAM, LPARAM);
WORD Comando;

/*  Make the class name into a global variable  */
char szClassName[ ] = "CodeBlocksWindowsApp";

int WINAPI WinMain (HINSTANCE hThisInstance,HINSTANCE hPrevInstance,LPSTR lpszArgument,int nCmdShow)
{
    HWND hwnd;               /* This is the handle for our window */
    MSG messages;            /* Here messages to the application are saved */
    WNDCLASSEX wincl;        /* Data structure for the windowclass */

    /* The Window structure */
    wincl.hInstance = hThisInstance;
    wincl.lpszClassName = szClassName;
    wincl.lpfnWndProc = WindowProcedure;
    wincl.style = CS_DBLCLKS;
    wincl.cbSize = sizeof (WNDCLASSEX);

    /* Use default icon and mouse-pointer */
    wincl.hIcon = LoadIcon (NULL, IDI_APPLICATION);
    wincl.hIconSm = LoadIcon (NULL, IDI_APPLICATION);
    wincl.hCursor = LoadCursor (NULL, IDC_ARROW);
    wincl.lpszMenuName = NULL;
    wincl.cbClsExtra = 0;
    wincl.cbWndExtra = 0;
    wincl.hbrBackground = (HBRUSH) COLOR_BACKGROUND;

    if (!RegisterClassEx (&wincl))
        return 0;

    hwnd = CreateWindowEx (
           0,                   /* Extended possibilites for variation */
           szClassName,         /* Classname */
           "B. Color changer (?)",       /* Title Text */
           WS_OVERLAPPEDWINDOW, /* default window */
           CW_USEDEFAULT,       /* Windows decides the position */
           CW_USEDEFAULT,       /* where the window ends up on the screen */
           240,                 /* The programs width */
           160,                 /* and height in pixels */
           HWND_DESKTOP,        /* The window is a child-window to desktop */
           NULL,                /* No menu */
           hThisInstance,       /* Program Instance handler */
           NULL                 /* No Window Creation data */
           );

    ShowWindow (hwnd, nCmdShow);

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


LRESULT CALLBACK WindowProcedure (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    static HWND hwndEdit,hwndEdit1,hwndEdit2;
    HFONT hFont;
    HDC hdc;
    PAINTSTRUCT ps;
    HBRUSH BackgroundBrush;
    RECT client_rect;
    static TCHAR text[4], text1[4], text2[4];

    switch (message)
    {
        case WM_CREATE:
            hwndEdit = CreateWindow(TEXT("Edit"), NULL, WS_CHILD | WS_VISIBLE | WS_BORDER,
              30, 25, 50, 20, hwnd, (HMENU) ID_EDIT_1,NULL, NULL);
            hwndEdit1 = CreateWindow(TEXT("Edit"), NULL, WS_CHILD | WS_VISIBLE | WS_BORDER,
              90, 25, 50, 20, hwnd, (HMENU) ID_EDIT_2,NULL, NULL);
            hwndEdit2 = CreateWindow(TEXT("Edit"), NULL, WS_CHILD | WS_VISIBLE | WS_BORDER,
              150, 25, 50, 20, hwnd, (HMENU) ID_EDIT_3,NULL, NULL);
            break;

        case WM_PAINT:
        {
            hdc = BeginPaint(hwnd, &ps);
            int len = GetWindowTextLength(hwndEdit)+1;
            int len1 = GetWindowTextLength(hwndEdit1)+1;
            int len2 = GetWindowTextLength(hwndEdit2)+1;
            GetWindowText(hwndEdit,text,len);
            GetWindowText(hwndEdit1,text1,len1);
            GetWindowText(hwndEdit2,text2,len2);
            GetClientRect(hwnd, &client_rect);
            BackgroundBrush = CreateSolidBrush(RGB(atoi(text),atoi(text1),atoi(text2))); //green background
            FillRect(hdc, &client_rect, BackgroundBrush);
            hFont = CreateFont(
                20, 10, 0, 0,FW_NORMAL, FALSE, FALSE, FALSE,
                ANSI_CHARSET,OUT_DEFAULT_PRECIS,CLIP_DEFAULT_PRECIS,
                DEFAULT_QUALITY,DEFAULT_PITCH|FF_ROMAN,"Verdana");
            SelectObject(hdc, hFont);
            SetTextColor(hdc,RGB(130,130,130));
            SetBkColor(hdc,RGB(atoi(text),atoi(text1),atoi(text2)));
            TextOut(hdc,13,70,"Inserta el color RGB",20);
            DeleteObject(hFont);
            break;
        }

        case WM_COMMAND:
        {
            InvalidateRect(hwnd, NULL, TRUE);
            Comando = LOWORD(wParam);
            break;
        }

        case WM_DESTROY:
            EndPaint(hwnd, &ps);
            PostQuitMessage (0);       /* send a WM_QUIT to the message queue */
            break;

        default:                      /* for messages that we don't deal with */
            return DefWindowProc (hwnd, message, wParam, lParam);
    }

    return 0;
}

        case WM_PAINT:
        {
            hdc = BeginPaint(hwnd, &ps);
            int len = GetWindowTextLength(hwndEdit)+1;
            int len1 = GetWindowTextLength(hwndEdit1)+1;
            int len2 = GetWindowTextLength(hwndEdit2)+1;
            GetWindowText(hwndEdit,text,len);
            GetWindowText(hwndEdit,text1,len1);
            GetWindowText(hwndEdit,text2,len2);
            GetClientRect(hwnd, &client_rect);
            BackgroundBrush = CreateSolidBrush(RGB(atoi(text),atoi(text1),atoi(text2))); //green background
            FillRect(hdc, &client_rect, BackgroundBrush);
            hFont = CreateFont(
                20, 10, 0, 0,FW_NORMAL, FALSE, FALSE, FALSE,
                ANSI_CHARSET,OUT_DEFAULT_PRECIS,CLIP_DEFAULT_PRECIS,
                DEFAULT_QUALITY,DEFAULT_PITCH|FF_ROMAN,"Verdana");
            SelectObject(hdc, hFont);
            SetTextColor(hdc,RGB(130,130,130));
            SetBkColor(hdc,RGB(atoi(text),atoi(text1),atoi(text2)));
            TextOut(hdc,13,70,"Inserta el color RGB",20);
            DeleteObject(hFont);
            break;
        }

        case WM_COMMAND:
        {
            InvalidateRect(hwnd, NULL, TRUE);
            Comando = LOWORD(wParam);
            break;
        }