So it would be possible to say "il ya des pois sur ces pois" - there are polka dots on these peas? ;-)
Why does the construction require "général" and not "générale"?
Because it defaults to masculine.
"In general do you prefer the stripes or the polka dots" was accepted.
It should not have been accepted. You cannot combine specifics with "in general".
"In general, do you prefer stripes or spots?" is also accepted.