You can change the folder colours in Linux Mint Nemo File Browser quite easily thanks to the community support. Follow the below instructions!
First we must install “Folder Color For Nemo” (the default file manager for Linux Mint Cinnamon desktops) and make sure we have an icon base that supports folder colours. The one i use is Papirus.
Open the Terminal app in Mint paste the following line.
$ sudo add-apt-repository ppa:costales/folder-color
Enter your password and wait for it to complete.
Do the same for the below commands too.
$ sudo apt-get update
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$ sudo apt-get install folder-color-nemo
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$ nemo -q
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The last command restarts Nemo so you don’t have to reboot. You should now be able to go to to any folder and right click and select a folder colour