Color: Walls are Mars yellow in distemper paint with calcium carbonate added. Floor: oil-based green paint.
Source: Courtyard of the Temple of Nerva Trajan as depicted in plate 15, Book 4 from Giacomo Leoni edition of The Four Books of The Architecture by A. Palladio
Although quite beautiful with its large circular windows and oculus skylight, the function of the Dome Room is not completely understood. The only known long-term occupants were Jefferson's grandson Thomas Jefferson Randolph and his bride, Jane Hollins Nicholas, who lived in the room for a number of months starting in 1815. By Jefferson's death, if not before, the room had become primarily a storage area.
Primary Source References
1807 April 18. (Jefferson to Richard Barry). "As the most important work you have to do here is to finish the floor of the hall and to paint the floor of the Dome room exactly in the same way." 
1809 August. (Margaret Bayard Smith). "We looked into a beautiful and circular room in the dome--it is 26 or 27 feet diameter--has eight circular windows and a handsome sky-light. It was designed for a lady's drawing-room when built, but soon found, on account of its situation in the dome, to be too inconvenient for that use, and was abandoned to miscellaneous purposes." 
1809 August. (Margaret Bayard Smith). “He [Jefferson] afterwards took us to the drawing room, in the dome 26 or 7 feet diameter—It is a noble & beautiful apartment—perfectly round with 8 circular windows & a sky-light—It was not furnished, & being in the attic story, is not used.—which I thought a great pity, as it might be made the most beautiful room in the house.” 
1812 March 16. (Jefferson to Henry Foxall). "I have a large dome room of 24. f. diam. which needs a stove, but a large one." 
1823 June 5. (Virginia Jefferson Randolph Trist to Nicholas Philip Trist). "I have never told you of the nice little cuddy that has become my haunt, and from which I am now writing. Do you recollect the place over the parlour's Portico into which the dome room opened? Since the columns to the portico have been completed, Grand-Papa has had the great work bench removed from it, and a floor layed. Corneilia's ingenuity in conjunction with mine formed steps from the dome into this little closet with a pile of boxes, and having furnished this apartment with a sopha to lounge upon, though alas! without cushions, a high and low chair and two small tables, one for my writing desk, the other for my books; and breathing through a broken pane of glass and some wide cracks in the floor; I have taken possession with the dirt daubers, wasps and humble bees; and do not intend to give it up to any thing but the formidable rats which have not yet found out this fairy palace." 
This eerie picture is from one of my favorite memories of working at Monticello, when we were just starting the Monticello Explorer in late 2003. To clarify, it’s not an actual photograph, in the...More >>