Both the bug fix for same-name-different-format, and the new optional placeholder display are working BEAUTIFULLY, thank you!!
As far as color display, I can display down to and including "Green", but the choices below that (Viridis-Plasma-Cividis-Terrain) do not display. This is with a Zerranoe 32-bit build of ffmpeg. But since we already have 11 working color choices, I don't see how anyone, even me, could possibly complain! I use Rainbow at any rate.
Note to others who want to try the "placeholder" image option: the image you choose will be expanded horizontally and vertically to fill the whole Spectrogram window area without respect to aspect ratio. Therefore, be sure you are using an image that either already has the dimensions of your Spectrogram window size, or is some pattern that looks OK to you when so displayed. Me, I just used Irfanview to reduce a favorite pic to the height of the specbox while keeping its aspect ratio, then added a black canvas the remaining size of the box around it (also with Irfanview) and save to png. Voila! Of course, you have to pretty much settle on your spec window size with that method, not that it's that big of a deal to create a new placeholder if your needs change.