Download using the GitHub .zip download option
Open your local MobaXterm.ini file. Depending on your install type, this can be located in either Documents\MobaXterm\MobaXterm.ini, or within your AppData which can be opened by entering shell:appdata\MobaXterm in the Explorer address bar or in the Run dialog (Windows+R).
Once opened, replace the [Colors] section with the contents of the MobaXterm.ini file you downloaded.
This will change the default color scheme - saved sessions will need to be recreated for it to take effect.