The word "white" has four forms in French. They are "blanc", "blanche", "blancs" and "blanches". Here are four phrases to illustrate these four forms:
une maison blanche (a white house)
les maisons blanches (the white houses)
un livre blanc (a white book)
les livres blancs (the white books)
With feminine nouns, the forms "blanche" and "blanches" are used while with masculine nouns the forms "blanc" and "blancs" are used. This is different from English which has the invariable word "white". In English, adjectives are not marked for gender nor number.
In many cases, the French feminine and masculines forms of an adjective are pronounced the same as in "bleu" and "bleue" (blue). In other cases, the final letter of the masculine form is silent while with the feminine the letter "e" is added and the consonant is then pronounced. (The final "e" can be pronounced as a schwa but is often silent). This is illustrated with "vert" and verte" (green).
With "blanc" and "blanche", however, rather than a feminine form in which the final sound is a velar plosive, the final sound is an alveopalatal fricative. How can we explain this?
It is possible that at one time the word "blanche" was pronounced similarly to the English word "blank". It is also likely the case that the word final "e" was pronounced. Since this "e" is a front vowel, it is plausible that the velar stop developed an advanced articulation. Also possible is that the hard "c" sound became the soft "c" sound in words such as "centre" and "cigar". If the pronunciation of the word "blanche" was once "blanke" which developed to "blanse", a phonological explanation can account for the change to "blanche". The "e" is a mid front vowel which can trigger palatalization. The high front vowel "i" is another which can trigger this palatalization process. It would be less likely to occur with a back vowel such as "u". In fact, European linguists often refer to front vowels as palatal and back vowels as velar.
A very literary account for the different pronunciations of "blanc" and "blanche" was given to me by a professor who taught me phonology as an undergraduate student. His explanation was so original and imaginative that I remember it to this day.
He suggested that we think of a planet in the sky. We know that the planet exists but on cloudy days we cannot see it. This relates to the form "blanc". We can see the word-final "c" but we do not pronounce it. Its silence is similar to the concept of an invisible planet. With the word "blanche", however, the sky is clear and the planet is fully visible. As a result, the word-final "c" of the word "blanche" is pronounced. It is initially pronounced as a velar plosive but becomes an alveopalatal fricative because the word-final vowel triggers palatalization. The pronunciation of the vowel relates to the concept of a visible planet.
This explanation may not exist in any textbook and may fail to impress many linguists, but I find it very descriptive and satisfying. It underlines that linguistics does not need to be a science which excludes art. On the other hand, it can be beautiful and creative. This is the reason I view linguistics as a combination of both science and art and not merely one to the exclusion of the other.