Mandrake – Some further research using Wikipedia:“Davis worked on the strip until his death in 1964, when Falk recruited current artist Fred Fredericks. With Falk’s death in 1999, Fredericks became both writer and artist. The Sunday Mandrake strip ended December 29, 2002. The daily strip ended mid-story on July 6, 2013 when Fred Fredericks retired, and a reprint of D220 “Pursuit of the Cobra” from 1995 began on July 8, 2013." I gather from this that the color strip is since 1999.
Mandrake – Some further research using Wikipedia:“Davis worked on the strip until his death in 1964, when Falk recruited current artist Fred Fredericks. With Falk’s death in 1999, Fredericks became both writer and artist. The Sunday Mandrake strip ended December 29, 2002. The daily strip ended mid-story on July 6, 2013 when Fred Fredericks retired, and a reprint of D220 “Pursuit of the Cobra” from 1995 began on July 8, 2013." I gather from this that the color strip is since 1999.