* Workers returned to factory on Monday - Merck spokesman
* Plant makes one-of-a-kind specialty automotive pigment
* Ford, Toyota, General Motors are customers (Rewrites with details, background on factory's customers)
TOKYO, April 5 (Reuters) - Germany's Merck KGaA aims to resume full production by June 1 in Japan at the world's only factory making a specialty paint pigment that has forced Ford Motor Co and other car makers to stop taking orders for cars in certain colours.
The chemical company closed its factory in Onahama soon after a magnitude 9.0-earthquake on March 11 damaged its facilities, disrupted infrastructure and crippled a Tokyo Electric Power Co nuclear power station about 45 km from the plant.
The factory is the sole producer of a specialty pigment called Xirallic that gives cars a glittering shine and is supplied to Toyota Motor Corp , General Motors Co and others. [ID:nN25285934]
Workers returned to the factory on Monday to begin repair and construction work with the aim of restarting production in stages before a full recovery from June 1, Merck's spokesman in Japan, David Pinsker, said.
Pinsker said he could not give a specific start date, or how much of the pigment would be delivered to which customers first.
The shortage prompted automakers last month to restrict orders on vehicles in certain shades of black, red and other colours.
Merck said the plant had been closed because some employees suffered damage to their homes and had difficulty commuting due to a gasoline shortage, and not because of radiation fears.
The Japanese government has established a 20-km (12 mile) evacuation zone around Tokyo Electric Power's Fukushima Daiichi complex, which continues to leak radiation after damage from the quake and tsunami. (Reporting by Chang-Ran Kim in Tokyo, Arpita Mukherjee in Bangalore; Editing by Edmund Klamann)