# Plotting Specific Color in DAGMC Void Cells

**URL:** <https://openmc.discourse.group/t/plotting-specific-color-in-dagmc-void-cells/5295>\
**Category:** User Support\
**Created:** [March 5, 2025, 8:16pm UTC](https://openmc.discourse.group/t/plotting-specific-color-in-dagmc-void-cells/5295 "2025-03-05T20:16:55Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![wrkendrick](https://avatars.discourse-cdn.com/v4/letter/w/59ef9b/32.png) [@wrkendrick](https://openmc.discourse.group/u/wrkendrick)\
**Post date:** [March 5, 2025, 8:16pm UTC](https://openmc.discourse.group/t/plotting-specific-color-in-dagmc-void-cells/5295/1 "2025-03-05T20:16:55Z")

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Hello all, I’ve got a odd question. I’m using OpenMC to plot my geometry that features a DAGMC Universe. In that universe are some empty regions. When I plot and \<color\_by=‘cell’\> it assigns a random color to these essentially void cells that I don’t have a cell-id for. Is there any way I can tell it what color to use? Right now it makes for an ugly plot if it randomly chooses something like magenta to use.

Thanks,  
Reed

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**Author:** ![wrkendrick](https://avatars.discourse-cdn.com/v4/letter/w/59ef9b/32.png) [@wrkendrick](https://openmc.discourse.group/u/wrkendrick)\
**Post date:** [March 5, 2025, 10:43pm UTC](https://openmc.discourse.group/t/plotting-specific-color-in-dagmc-void-cells/5295/2 "2025-03-05T22:43:50Z")

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Patrick Shriwise answered this for me: The dev branch of OpenMC (as I’m writing this) has a model.sync\_dagmc\_universes() feature, which then lets you call model.geometry.get\_all\_cells(), that way you know what cell-id the empty cell is!

Additionally, if you need a quick workaround like I did, the empty cell will be assigned an id one greater than the last volume id in the mesh. So for me, my last volume had an id of 41428, so I added a color for cell\_id=41429 to my plotting color dictionary and it seems to have worked.