text: Title: Unsharp Mask on RGB Image Results in Black Image When channel_axis Specified
  Body: ### Description:
  
  When applying `skimage.filters.unsharp_mask` to an `RGB` image and specifying the `channel_axis`, the resulting image turns black. However, if `channel_axis` is not specified, the issue does not occur. This issue appears to be specifically related to the handling of the `channel_axis` parameter.
  
  ### Way to reproduce:
  
  ```
  from skimage import data, filters, color
  import matplotlib.pyplot as plt
  
  # Load an RGB image
  rgb_image = data.astronaut()
  
  # Apply unsharp mask
  unsharp_rgb = filters.unsharp_mask(rgb_image, channel_axis=-1)
  
  # Display the images
  plt.subplot(1, 2, 1)
  plt.imshow(rgb_image)
  plt.title('Original RGB Image')
  
  plt.subplot(1, 2, 2)
  plt.imshow(unsharp_rgb)
  plt.title('Unsharp Mask RGB Image')
  
  plt.show()
  ```
  
  ### Version information:
  
  ```Shell
  3.9.6 (default, Mar 10 2023, 20:16:38) 
  [Clang 14.0.3 (clang-1403.0.22.14.1)]
  macOS-13.3.1-x86_64-i386-64bit
  scikit-image version: 0.22.0
  numpy version: 1.26.2
  ```
  