I like the question. Until and unless the person who chose it wishes to answer, here's my attempt at a more-than-complete answer.

I guess orange may be chosen as a rather eye-catching color. A reddish orange may be chosen to be a bit more tasteful or distinctive.

The choice of RGB component values may originate in an older practice in web design called web-safe colors (http://en.wikipedia.org/wiki/Web_colors#Web-safe_colors). It uses the observation that 33 hexadecimal (let's write 0x33) evenly divides the range of an HTML red-green-blue color component: 0x00, 0x33, 0x66, 0x99, 0xCC, 0xFF. Choosing each of the three color components from among these six values yielded 6^3 = 216 colors, a palette that would fit into a low-end graphics adapter's table of 256 colors with room left over for system-defined colors.

Those who have studied Mersenne primes may recall that it is sufficient to observe that 8 is a composite number in order to prove that 0xFF = 0x100 - 1 = 2^8 - 1 is a composite number. And we compute that 2^8 - 1 = 255 which ends in 5, so it's obviously divisible by 5, the quotient being 51 = 0x33.

It's Paul's favorite color. It's also the color of the walls at YC.

Because YC.

Why not?