No really why not just change it to mood?
Mood is too wide for 'Joy'. I liked fun rather than joy anyway because Sims series also had 'fun'.
IMO Mood makes sense. Joy maybe not. Low Joy /= Hate or Dread. Just means you're not having lots of fun.
Mood is too broad. While a low Joy means you're not joyous, the goal and the activities are to do joyous stuff and to be joyful, not to be 'mood'.
Fun is too specific. Not every joyful activity are exactly fun or funny. A walk in the park or stargazing are not necessarily fun/ny, but might bring joy.
Joy seems about right for me, unless a better one comes around.
Different gameplay mechanic from the look of it.
Mood is meant to be a critical stat varying over short period of time.
'Joy' seem meant to fill up only positively, bringing a bonus to Mood but over longer period of time.
Meaning that a 'joy-full' colonist could stay ok over long period of spontaneous amputation, whereas a 'joy-less' colonist would need a strong will and still be on the brink.
I would not be surprised if Tynan made mood harder to keep right to emphasize the 'Joy' part.
So, when will we get the Social, Toilet and Hygiene meters as well?