緑 and 黄色: color-specific modifying forms
Connect green and yellow to objects while recognizing that color names form modifiers differently.
Expressing green
緑, read みどり, means green. 緑の葉が見えます。 says that green leaves are visible.
緑のかばん is possible, but simply adding い to make 緑いかばん is not. Color names do not all form adjectives in the same way.
Expressing yellow
黄色, read きいろ, means yellow. 黄色い花が咲いています。 says that yellow flowers are blooming.
黄色の花 is also possible. Learn both 黄色い and 黄色の, and retain the long きい in the reading きいろ.
What has the color and how it changes
葉は緑ですが、花は黄色です。 says that the leaves are green but the flowers are yellow. Keep each color paired with its object.
葉が緑から黄色に変わりました。 says that the leaves changed from green to yellow. から marks the original color and に the resulting color.
Can every color name take い, as in 緑いかばん?
Show the answer and why
No. Use 緑のかばん. Distinguish this from a valid adjective form such as 黄色いかばん.