That's actually pretty much all it takes, Teddy. Solo_bones and I initially dropped the colored film just behind Threepio's eye grills and in front of the white translucent piece that his pupils are painted on. But when he's "shut down," his eyes should be white, so it's actually more accurate to place the colored film
behind this piece, like so:
BTW, bless you guys who are content to keep your figure just the way it is out of the box. But, for us perfectionists, here's something I chanced upon while visiting my local theater supply store: a free professional lighting gel swatch book!
I thought the cellophane and file folders seemed too low-rent to use on such a high-end item like this, so I went looking for a place that sells photographic lighting gels, hoping to buy a single sheet in a suitable shade of amber. Turns out, you can get a complementary swatch book of 1 3/4" x 3" sheets of this material, which includes about a dozen or so different shades of amber that should look just fine on this figure.
(Of course, it may drive me crazy finding the perfect hue to use for Threepio's eyes. Talk about an embarrassment of riches!)