How about just 1x1? Using the standard RGB color space there are 16,777,216. I doubt HN will have that many users so everyone gets their own color :-)

Your design is not future-proof.

Sure it is, just add another pixel :)

"Look at that 3 pixel noob..."

You could use the user's top bar preferences!

only the elite have the privilege of changing the topbar color.

Only the elite deserves their very own pixel.

(I recently joined the elite - that's why I'm smug.)

...or 10 x 1. Even with only 32 colors per pixel, that's over a quadrillion color combinations.