How to count the number of occurrences of an item in an image?

I have a series of images that display plastic shapes of different colour that looks like this:

There can be several of the same shape and colour (eg. multiple blue squares). I also have a template image:

I want to count the number of occurence of the template image in the image.

This is what I have tried so far, which creates a binary image of only the blue shapes:

I = imread("im1.jpg");
template = imread("blue_square.jpg");

Ired = I(:,:,1);
Igreen = I(:,:,2);
Iblue = I(:,:,3);

blueOnly = Iblue - Ired - Igreen;

se = strel('disk', 15);
blueBin = imfill(imerode(imdilate(blueOnly, se),se),'holes');