It’s behaving correctly. If you want a texture that “looks gray” you’ll have to convert/save the png in an RGB format. But that’d just waste memory since for gray all channels contain the same values and ValueMap uses only one channel of the texture anyways. Have a look at its rightmost pin.
Thanks a lot for the explanation. Strange I did not realize this before. But probably so far most textures I used where saved in RGB instead of Grayscale. This post might be moved to “questions” then. ;)