The Black Book of Colors by Menena Cottin is wonderful for fostering creativity in your students. Each page of the book describes a color. The 'illustrations' are raised/embossed shapes on the page. Each sentence is also written in braille on each page.
The author describes each color by talking about things that are that color and what it is like. "Green smells like grass that's just been cut" is a great example of the type of description this book has written inside.
This book combined with Hailstones and Hailbut Bones would be a great way to have students practice describing colors. Students could also gather pictures (either magazines or real photos) of things that are a particular color and as a class turn their short descriptive phrases of the color into a class poem about each color.
For younger students to practice writing, make a class book with labels. Each page of the class big book could have the title, "Things That Are Red" or "Things That Are Yellow" - students add pictures and label each picture to show the items that they added.