Hello
I am Abdal and I would be glad to help you with your question.
There could be a few different reasons why your custom color theme might not be applying to one of your presentations. Here are a few things you could try:
Check the slide master for the presentation that is not accepting the custom color theme. The slide master is a template for all of the slides in your presentation, and it could be set to use a different color theme. To check the slide master, go to the "View" tab and click on "Slide Master".
Make sure that the custom color theme you are trying to apply is compatible with the version of PowerPoint you are using. If the presentation that is not accepting the custom color theme was created in an earlier version of PowerPoint, it might not be compatible with the version you are using.
Check to see if the presentation that is not accepting the custom color theme has any custom colors defined within it. If it does, these custom colors could be conflicting with the colors in your custom color theme. To check for custom colors, go to the "Design" tab and click on "Colors" in the "Themes" group. If you see any colors listed under "Custom Colors", you may need to delete these before you can apply your custom color theme.
I hope this information helps.
Regards,
Abdal