I have two holes under the speedo and the blank on a 55 burb carryall dash. I saw a pic of a finished truck and the left hole had a red lense and the right a green one. What are these and why does mine not have the lenses?

"Upon the plains of hesitation bleach the bones of countless millions, who when on the dawn of victory paused to rest, and there resting died." - John Dreschmer