void GradientTriangle( HDC MemDC,
    LONG x1, LONG y1,
    LONG x2, LONG y2,
    LONG x3, LONG y3,
    COLORREF top, COLORREF bottom )
{
    TRIVERTEX vertex[3];

    vertex[0].x     = x1;
    vertex[0].y     = y1;
    vertex[0].Red   = GetRValue(bottom) << 8;
    vertex[0].Green = GetGValue(bottom) << 8;
    vertex[0].Blue  = GetBValue(bottom) << 8;
    vertex[0].Alpha = 0x0000;

    vertex[1].x     = x3;
    vertex[1].y     = y3;
    vertex[1].Red   = GetRValue(bottom) << 8;
    vertex[1].Green = GetGValue(bottom) << 8;
    vertex[1].Blue  = GetBValue(bottom) << 8;
    vertex[1].Alpha = 0x0000;

    vertex[2].x     = x2;
    vertex[2].y     = y2;
    vertex[2].Red   = GetRValue(top) << 8;
    vertex[2].Green = GetGValue(top) << 8;
    vertex[2].Blue  = GetBValue(top) << 8;
    vertex[2].Alpha = 0x0000;

    // Create a GRADIENT_TRIANGLE structure that
    // references the TRIVERTEX vertices.

    GRADIENT_TRIANGLE gTriangle;

    gTriangle.Vertex1 = 0;
    gTriangle.Vertex2 = 1;
    gTriangle.Vertex3 = 2;

    // Draw a shaded triangle.

    GradientFill( MemDC, vertex, 3, &gTriangle, 1, GRADIENT_FILL_TRIANGLE);
}

// bottom triangle --> need help with this one!!
    GradientTriangle( (HDC)wParam,
        r.left, r.top,
        r.left, r.bottom - r.top,
        r.right, r.bottom - r.top,
        RGB( 0x0, 0x0, 0xFF ), RGB( 0xFF, 0xFF, 0x0 ) );

    // top triangle --> this one is fine !
    GradientTriangle( (HDC)wParam,
        r.right, r.bottom - r.top,
        r.right, r.top,
        r.left, r.top,
        RGB( 0xFF, 0x0, 0x0 ), RGB( 0x0, 0xFF, 0x0 ) );
}
return 1L;

// I have modified parametters for bottom triangle
GradientTriangle( (HDC)wParam,
    r.left, r.top,
    r.right, r.bottom - r.top,  //  switched places
    r.left, r.bottom - r.top,   //  of these two coordinates
    RGB( 0x0, 0x0, 0xFF ), RGB( 0xFF, 0xFF, 0x0 ) );  // but color has changed