The appropriate word to fill into the blank would be accessory.
In the Fall of the year, leaves appear red, orange, yellow, and brown because the chlorophyll decreases in the leaves and allows the accessory pigments to reflect mostly colors other than green.
The core pigment in leaves that makes them appear green is chlorophyll. The pigment is primarily responsible for absorbing light energy to drive the photosynthetic process in plants.
Some other pigments, also known as accessory pigments such as carotenoids, anthocyanins, xanthophylls, etc., help out chlorophyll in some ways but have colours that are different from green.
Thus, the appearance of other colours such as orange, yellow, brown, etc., on leaves is due to a decrease in chlorophyll and the reflection of the colours of the accessory pigments.
More on accessory pigments can be found here: https://brainly.com/question/3405710?referrer=searchResults
