If you use image editing software to colour your mindmap branches or images you may like to create a colour sheet for colours you like and those that you use regularly.
You can open your colour sheet image in your image editing software, select colours to use in your mind map and add new shades whenever you see or use a new colour.
Maintaining a colour sheet allows you to add tones and shades not in your regular palette of your image editing software.
I have shared here my colour sheet which you are welcome to download and use - you can add to and amend it for your own use.
Also provided is a blank version if you prefer to collect your own colours.