Is your feature request related to a problem? Please describe.
E.g. I'm using pseudocolor to visualize anthocyanin content (ARI). It is only possible to have a white, black or input grayscale as background. I would love to have either an RGB image or a monochromatic image which is not the index reflection result as background.

Describe the solution you'd like
Add and option/input for an image that will be uses as a background. E.g. like this:

plantcv.visualize.pseudocolor(gray_img, mask=None, background="image", bg_image=None, cmap=None, min_value=0, max_value=255, axes=True, colorbar=True, bad_mask=None, bad_color="red")

If background="image" and bg_image=None the gray_img will be used as background
If background="image" and bg_image=bg_img the bg_img will be used as background

Describe alternatives you've considered
Of course, this can be done outside plantCV using the original matplotlib functions. I just think it might be convenient and useful to more users.

I can implement this if you all think it makes sense.

Here is an example made with matplotlib