Rated 2 out of 5 stars

Although I absolutely love the idea I did not found any theme I liked too much and the default ones can screw with functionality on some websites.

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

You are encouraged to compose your own default theme using the basic HSLA transformations.

> The user informed me that he would like to impose certain text or background colors on input elements.

'Color Transform' and 'Colorific' cannot target elements of a specific type. Your best bet is to add specific CSS rules using e.g. 'Stylish', 'User Style Manager' or 'Color That Site'. Given that input elements normally don't contain background or foreground images, it should be possible to obtain a readable result.

> The user informed me that the lack of contrast in most themes led to e.g. indiscernible rating stars.

Color Transform and Colorific are not meant for contrast enhancement, but mainly for darkening pages in order to reduce eye strain in dark environments. However, Colorific's single-spectrum themes retain quite a lot of contrast, while e.g. a mere brightness inversion in Color Transform retains all contrast.

The deeper reasons for the reduced contrast in most themes of Color Transform and Colorific are the following:
Background colors cannot simply be set because they need to be matched to background images. Images require non-constant transformations in order to retain contrast. These transformations are always narrowing down the range of colors if they are to have a similar effect on both bright and dark pages. It is not possible to determine whether a page is predominantly bright or dark without rendering it, and even after that it is hard to estimate. In addition, it is impossible to determine whether text is shown on top of one or more elements which have a CSS background image. Hence it is safe to set text and background colors directly to values with high contrast only if one also hides all CSS background images. In most cases this is unacceptable, because these images have many uses on modern pages as icons and other art work.