Michelangelo owned a pomeranian who famously watched him paint the
ceiling of the sistine chapel, what colour was this dog?

It was probably a mixture of the colours that Mike had splashed around.

Painting a ceiling is notoriously messy.

Hello,
The volpino italiano, Michelangelo's dog's breed, might have been a
white colored dog (or, not probably, red or champagne):

"Durante il rinascimento questo piccolo e intelligente cane ha
decorato le corti della nobiltà e ha tenuto compagnia anche a
Michelangelo."
(During Renaissance, this little smart dog has decorated nobility
court and was a company for even Michelangelo)(my translations)
"gli artisti del rinascimento anno dedicato le loro tele a questo
piccolo cane bianco"
(Renaissance artists have dedicated laurels to that tiny white dog)
http://www.inseparabile.com/cani/volpino_italiano.htm

"Il Volpino Italiano (non "mediterraneo") è un piccolo cane bianco, dal pelo lungo"
(The volpino italiano (Not mediterranean) is a little white dog, with long hair)
"Era il cane preferito di Michelangelo."
(It was Michelangelo's favorite dog)
http://genio.virgilio.it/genio/cgi/risposte.cgi?idcan=10&idquest=15081

"Volpino italiano - COLOR: Pure white or sable (rare)"
http://www.thebreedsofdogs.com/VOLPINO_ITALIANO.htm

luntes

Interesting!

I haven't been able to find a definitive answer, so here are my
comments on the matter.

I think the answer is "If Michelangelo had a 'Pomeranian' it was probably white"

Michelangelo painted the Sistine Chapel between 1508 and 1512. At that
time pomeranian dogs didn't exist as we think of them today. The
predecessor of the Pomeranian was a wolf/spitz type of dog, which
weighed about 30 pounds and was usually white.

See:

"The Pomeranian is believed to have descended from wolf-spitz type
dogs which at some early period migrated to Pomerania from the north
of Russia and Siberia.Sharing the same ancestors with the other arctic
breeds such as the Samoyed and Keeshond. These early spitz type dogs
were used to work as guard and sledge animals,however the smallest
were kept as companions. At this stage of development,the breed
weighed 30 lbs and were coloured white, black or cream. Pomeranians
were established as a breed in the eighteenth century after they drew
the interest of the English monarchy. Upon her marriage to King George
III, Queen Charlotte brought large white Pomeranians to England in
1761. Gainsborough often included dogs in his paintings. The
pomeranian appears in many of his compositions. The Prince of Wales
had a white and black Pomeranian he called Fino. The animal was
painted twice by George Stubbs."

http://www.georgianindex.net/dogs/dogs.html

 

Also:

"Queen Charlotte acquired several White Spitz dogs weighing between 20
to 30 pounds from Pomerania. The German's disapproved of the erroneous
term "Pomeranian" being used to describe the White Spitz dog. These
were not the same dog which is recognized today as the Pomeranian.

Thomas Gainsborough (1728-1788) depicted the White Spitz dog in
several paintings, most notably "Pomerania Bitch and puppy", "The
Morning Walk", and "Mrs. Robinson".

Color and size changes began in England with the influence of Queen
Charlotte. With the ascent to the throne of Queen Victoria, the breed
would be changed forever. The forerunner of the toy breed "Pomeranian"
we know today would begin to emerge."

Pictures from the 18th century of Pomeranians: (mentioned above)

"Pomerania Bitch and puppy"

http://www.boxcarbailey.com/pomerania.htm

"The Morning Walk"

http://www.boxcarbailey.com/themorningwalk.htm

"Mrs. Robinson"

http://www.boxcarbailey.com/mrsrobinson.htm

Very best regards

THX1138

I think luntes might have got it right! 

"Volpino Italiano

Also known as the Italian Spitz, the Volpino Italiano closely
resembles the Pomeranian and is often mistaken as such. It originally
was a pet for the Italian gentry and a watch dog for the working
class, but today is a lively and devoted companion dog. Its common
coat colors include white and champagne."
http://www.boxcarbailey.com/spitzbreeds.htm

Very best regards

THX1138