Vimeo video with Embedder plugin
Author of the plugin here - @Lindsey is correct - wrapping the color in quotes is the correct syntax. If you test it with this video, it works fine:
https://vimeo.com/130900978

One thing to note - with Vimeo, a video owner can overwrite this option - so if they set it to a specific theme color, you can't change it through this embed parameter. For more info on the Vimeo API, you can see this documentation: https://developer.vimeo.com/player/embedding