28 October 2017
I just double-checked this in case there was a bug in value painting (I haven't used it in quite some time), but no; it's working fine.
When you switch to value mode the voxels change to a greyscale colour mode. The brightness of the greyscale indicates the value of the voxel from 0 (black) to 255 (white). So when you paint with the selected value, it looks like you're changing the colour, but you're actually only changing the value.
When you're finished painting values, simply change the dropdown from Value back to Color and the colours will return to normal.
There is one slight bug that I did notice: if you click Stop Editing while still in Value mode, the colours will not change back as they should, and will remain greyscale. If that happens, click Start Editing, then change the dropdown from Color to Value and then back to Color again, then Stop Editing.