Hi James 

Thanks for posting in the community! It is intended Mind Map functionality for nodes added in different levels to be distinguished by different colors. To set a default color for every single node in the mind map you can individually set the same color for the root and each layer in the Mind Map toolbar and not with the general fill color tool as this will be overridden by your Mind Map color selections. This can be accomplished by selecting the entire Mind Map, selecting ‘filter objects’, then selecting ‘lines’. You will then be able to select the color you would like all of your lines to be.

Currently disabling root and level colors is not supported in Lucidchart but if this is something that you'd like to see in the future please add your thoughts to our product feedback space. For more information on working with mind maps please view our Mind Mapping article from our Help Center as a resource and let me know if you have any additional questions. Hope this helps!