The adjective colorless can be understood as dull, uninteresting, or lacking in color, and so when it combines with the adjective green, this is nonsensical: an object cannot simultaneously lack color and have the color of green. In the phrase colorless green ideas the abstract noun idea is described as being colorless and green. However, due to its abstract nature, an idea cannot have or lack color.
The adjective colorless can be understood as dull, uninteresting, or lacking in color, and so when it combines with the adjective green, this is nonsensical an object cannot simultaneously lack color and have the color of green In the phrase colorless green ideas the abstract noun idea is described as being colorless and green. However, due to its abstract nature, an idea cannot have or lack color.