# ValueError: 'viridis_r' is not a valid value for cmap; supported values are: 'viridis', 'plasma', ...

- **ID:** `python/matplotlib-cmap-not-recognized`
- **Domain:** python
- **Category:** config_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

Passing a colormap name that matplotlib does not recognize, often due to a typo or a colormap registered by a different library (e.g., cmocean) that is not installed.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| 3.x | active | — | — |

## Workarounds

1. **** (95% success)
   ```
   import matplotlib.pyplot as plt
print(list(plt.colormaps()))
ax.imshow(data, cmap='viridis_r')
   ```
2. **** (90% success)
   ```
   pip install cmocean
import cmocean
ax.imshow(data, cmap='cmo.thermal')
   ```

## Dead Ends

- **** — Falls back to the default colormap, silently changing the intended visualization. (80% fail)
- **** — Also invalid; the correct suffix is '_r'. (90% fail)