I just received the most recent edition of The Star Magazine. It is the official magazine of the Mercedes-Benz Club of America.
In the Technical Tips section, compiled by Stu Ritter, there is a short paragraph on coolant:
"In 1999 the factory began using two kinds of engine coolant anti-freeze. The original is tinted yellowish, and the new one is tinted bluish. Both are compatible with each other."
Both the yellow and the blue coolant are available in the U.S.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".