It's not strange for color plates to vary in tone in various printings of Oz books. Accidental changes can happen from one printing to the next, and sometimes deliberate changes are made, especially when trying to cut publishing costs.
The example above shows how drastic changes can happen when a book changes publisher. The illustration by W. W. Denslow shows Dorothy and friends meeting the Cowardly Lion for the first time, in The Wonderful Wizard of Oz. On the left is the original version of this color plate, as published by George M. Hill in the first edition. The center image shows the change that happened when Bobbs-Merrill began publishing The New Wizard of Oz. The color plates in the new edition lost much of the original clean brightness seen in the Hill edition, and became slightly muddied. The final plate is from a 1939 copy of The Wizard of Oz, also published by Bobbs-Merrill. This plate does have three colors in it, but it hardly seems worth the bother!
An interesting, and I think more unusual, change happened during the print runs of The Marvelous Land of Oz. Around the 4th state, the color plates became much brighter than in earlier issues. Off hand, I don't think any other Oz books published by Reilly & Britton had this kind of dramatic alteration. The publishers must have felt that the brighter colors were more appropriate to the story.
Incidentally, this illustration is another example of John R. Neill using curtains for dramatic effect!