Encoding images to webp on iOS regardless of the color space?

Question

I'm trying to convert any picture to WebP on the fly but I have a lot of trouble with images that have a color space that isn't RGB: it's grayscale (kCGColorSpaceModelMonochrome).

Is there an existing WebP library or class that will convert non-RGB images to WebP? Or is there any way I can convert a non-RGB image to an RGB image programmatically so I can modify the WebP class that I already have?

Thanks!