I may be alone here, but I think the blank version is best as is w/o the novelty keycaps. I have the red escape key for my hhkb2 but don't use it because it's a little "ooh, look at me, I'm different". You don't see the the most expensive and classy cars with red rear view mirrors mounted on the windshield or purple AC controls on the dash. I honestly think the Japanese designer of the hhkb2 has more insight into what would look best aesthetically. Don't get me wrong, I think the red escape key is cool and purple WASD keys are something I plan to get (I'll keep them with my red esc key that I keep in the HHKB box), but I think it looks it's absolute best as is w/o colored keys.
I personally chose the white version as it was two toned, and would show keycap wear less than a black kb would. As for yellowing, when mine does, I won't mind so much. Most classic looking computer hardware has yellowed over the years, and I expect mine to age well, as well. I care more about texture consistency, scratches, dents, scraps, etc.
If there was a set of double shot keys made for the HHKB, that'd be nice, but I really don't like the inconsistency of some keys having print on the side, and others don't.
For anybody interested in making a purchase of the HHKB, go for it. It was my first mechanical keyboard purchase, loved it, and haven't really felt the need to try any of the other modern offerings.
