Now that the yellow goodness has arrived (thanks again, Prof!), here is the usual comparison:
From left to right:
1. WASD sampler kit
2. KeyPop awesome face
3. Ducky key chain keycap
4. Hazard set
5. KeyPop Smile!
6. Topre
7. Filco
In that shot the Filco does look a bit orangish, which is the general impression I got from most of the pictures I have seen of these keycaps. This is totally fine by me
Now that I see Filco next to SP yellow, the SP one seems to have a slight green tinge to it. WASD still seems faded, and Topre is, well, at a guess I'd say slightly orange like the Filco, but with a shade of blue too. Or maybe it was a trick of the light ...
Another way of showing it is to put the other yellow keycaps on the keyboard, alternating between the Filco yellow (same order as above):