Abstract: The present invention relates to compositions useful for the detection of oxygen in a humid medium, characterized in that they comprise at least one complex of the formula (LMX).sub.n in which the ligand L is selected from among the groups: ##STR1## where: R represents Cl,Br,NO.sub.2,C.sub.1-4 -alkoxyl, C.sub.1-4 -alkyl,m and p are comprised between 0 and 3,q is comprised between 0 and 2,the substituent R on the pyridine nuclei never occupying a position neighboring the nitrogen atom,X=Cl,Br,I,NO.sub.3,C10.sub.4,M represents Cu or Mn, andn is equal to 1 or 2,as colored indicator of the presence of oxygen in a humid medium, in solution in an acceptable solvent.The present invention also relates to a process for preparing such compositions, and detectors of the presence of oxygen comprising them.