Platinum Usage and Color

Greetings. A couple of related questions.

Went to an exclusive Estate Jewelry shop in Las Vegas and in looking
at some turn of the century pieces got the following answers to my
questions.

The headband is silver plated gold. I can imagine this being done to
match the diamond settings but not the entire piece. Anyone have an
idea why this might be done?

Was also told that platinum was not workable in late 1800/ early
1900’s. I believe I have seen some rather outstanding Art Nouveau
pieces in platinum. Any comments on when platinum was used as jewelry?

Bill in chilly Vista