Rated 5 out of 5 stars

This is the best working add-on in that category.
There are cases where I would like to have some hue variations within a page, though. For example this review page, setting the stars in the rating did not show. What annoys me the most is that visited and unvisited links look exactly the same, if there is a solution for that I'd be glad to hear it.

This review is for a previous version of the add-on (4.9.1-signed). 

The main reason for the limited contrast in the themes of Color Transform is that this ensures that more or less the same result is achieved on dark and bright pages. Simple transformations such as brightness inversion will retain most contrast, but these do not give you control of the resultant colors (for example, dark pages will become bright).

One of the underlying problems is that almost all modern pages use css 'background-image' styles both for backgrounds behind text and for foreground icons/images (such as stars). A theme may now either limit the background colors to a certain range or it may retain the contrast in background images, but it cannot do both.

However, my add-on Colorific contains several single-spectrum transformations that yield higher contrast but less control of the background color. Also, Colorific gives you freely designable themes, so you may try to find a better solution yourself.

For distinguishable link colors, the best solution is to increase the initial contrast in those colors in the Firefox content options.