That's interesting - I wasn't aware of IndigoMax using Max gamma. Although to be fair, it was more of an issue in the early version of IndigoMax compared to now.
But there is a quick test that can be recreated - open GIMP/PS and make a new image with a solid colour (for example 190, 0, 0).
Making a new material and using the colour picker to pick the solid colour, with gamma off, picking the colour it reads back as 190, 0, 0.
With gamma on, picking the colour, Max reads back 133, 0, 0.
If I then leave gamma on, and render, then Indigo renders the colour as if gamma is off in Max. The log window reads Master gamma: 1.0.
I then verify this by using the Pick Material in Indigo, and comparing the swatches in Max and Indigo. And they are different.
So if a client asks for a specific shade of colour for an interior wall for example with a swatch, I usually use the colour picker. But then I get confused, because the output is different in the Material Editor and in Indigo.
Unless I'm misunderstanding how gamma works.
Max's gamma options can be found at Customize - Preferences.