There are two differences between the grey and white versions.
-the white has a cut-out in the round foot. This allows it to be rotated into place, such a hole with a smaller diameter.
-the grey without the cut out can only be retained by a slot in the panel.

The 4 spaces between the 'legs' are identical on the grey one, whereas the white has two spaces opposite one another that are shorter, which probably makes it a bit stiffer and so a tighter fit.

They are both the same length,diameter, and fit in the same diameter/slot.

As an aside some earlier models had a pale green version, to fit a fractionally thicker panel that had the cut out in the foot like the white, and the spaces like the grey!

So now you know...