I posted the following in the Philco forum:

I was looking for a Hippo and I've seen 2 different knob styles. One with gold embellishment at the base of the knobs and one with plain brown knobs.

Did Philco make a change in production or did the plain ones have the gold removed?

Thanks.

I think it just wears off. When I did a Hippo for my sister there were only very tiny remnants of the gold paint remaining on the knobs.