Showing gray image in picturebox in Visual studio c++

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Hi all, I am trying to do some gui to show original image, gray, blur, and other things with visual studio c++ WinForms. I wanted to show the mat images in picturebox and I found some examples to do it. I can show images in picturebox now. However when I try to shown gray scale image in picture box, I get different color additional to gray image. I see different colors. I also open gray image with imshow, There is no problem with image. I think conversion keeps other 2 channels. I have searched very long time but I could not find any answers for my problem.

I tried to add a link which shows result of my gui. However my karma is not enough to share link

all Suggestions are appreciated.

System::Drawing::Image^ OpencvReadPicture() {
    cv::Mat originalImage ;
    originalImage = cv::imread("banana.jpg", cv::ImreadModes::IMREAD_COLOR);
    cv::imshow("OriginalImage",originalImage);      
    System::Drawing::Bitmap^ bitmap = gcnew System::Drawing::Bitmap(originalImage.cols, originalImage.rows, originalImage.step, System::Drawing::Imaging::PixelFormat::Format24bppRgb, System::IntPtr::IntPtr(originalImage.data));
    System::Drawing::Image^  image = static_cast<System::Drawing::Bitmap^>(bitmap);     
    return image ;
};
System::Drawing::Image^ OpencvGrayPicture() {
    cv::Mat grayImage;      
    cv::cvtColor(originalImage, grayImage, CV_BGR2GRAY,1);      
    cv::imshow("GrayImage", grayImage);     
    System::Drawing::Bitmap^ bitmapGray = gcnew System::Drawing::Bitmap(grayImage.cols, grayImage.rows, grayImage.step, System::Drawing::Imaging::PixelFormat::Format8bppIndexed, System::IntPtr::IntPtr(grayImage.data));
    System::Drawing::Image^  imageGray = static_cast<System::Drawing::Bitmap^>(bitmapGray);
    return imageGray;
};
pBoxOriginalImage->Image =OpencvReadPicture();// showing original image in the picture box.
pBoxGrayImage->Image = OpencvGrayPicture();// showing gray image in the picturebox.