may be use hsv or lab colorspace to segment，such as
im = imread('https://ww2.mathworks.cn/matlabcentral/answers/uploaded_files/917019/8.jpg');
jm = rgb2hsv(im);
s = mat2gray(jm(:,:,2));
s = imcomplement(s);
h = mat2gray(jm(:,:,1));
bw = imbinarize(s,'adaptive');
bw = bwareafilt(imfill(imclose(bw, strel('disk', 10)), 'holes'),1);
bw2 = imbinarize(h,'adaptive','ForegroundPolarity','dark','Sensitivity',0.9);
bw2(bw) = 0;
figure; imshow(im);
hold on; h = imshow(label2rgb(bwlabel(bw)), []);
set(h, 'AlphaData', 0.5)
