SUMMARY While I have been drawing, I have noticed that lowered opacity image where the reference image is white is intrusive to my drawing. To explain, I couldn't explain why painting isn't fully black at first until I realized the reference image had a opaque background. So, onto the feature request to solve this issue. Color to Alpha option for reference image with alpha normalization option. Invert Image also should be a option within reference image. These two built-in features would help avoid this issue, and make drawing more streamlined when using reference image as some sort of drawing reference. While yes, artists can edit those reference image, it wouldn't be as flexible as something like this for the purpose of using those as tracing helper. Software - Krita e6f675a - OS independent because it's not part of Krita.
Also, I think there's a few more use case of this. Let's say you're working from making sketches based on colored blueprint and you want it as a reference layer instead. This can save time. I wouldn't say this is a needed feature, but it would be nice to have more flexible workflow which is something I enjoy about Krita.