You sent an administrator and me a PM a few hours ago asking to change the color scheme.
I'm just some newbie here (less than a year active) and i can't be of any help with that, but also i can't say i'm having any difficulty reading this site.
I spend at least an hour a day over here and can't say i feel fatigue because of that.
But i'm assuming you are right and backed by some research.
I'm not a youngster, and i'm not old (but that youngster might think different about that).
You said "to make things readable" and "one must design...", and that implies the site is impossible to use and also implies there would be some standard any website has to comply to.
A recommendation is an advice one can consider or omit.
Words like "must" and "have to" don't look like a recommendation to me, more like an order to change something.
My recommendation would be to add an extra style for the forum (i'm not sure if this can be used for the entire site) for people that have trouble reading it.
I know other forums offer different styles to be chosen by the user, but don't know the "simple machine" software allows such options.
Neither do i know if and how how troublesome it would be to offer multiple styles.