Hi,
I hope the remains of sticky can provide their great wisdom.
I try to use zwift with my IRL weight, but last year, since I synched my zwift account to zp, I lost 2kgs close to 4lbs I believe… idk), the thing is that since I keep updating my weight changes (I use weekly average, since we all have a ±1.kg per day/week) but when I check my race results my weight is shown ir red numbers when it’s lower… i.e. I started racing with 61kg, but now I weight 60, 60 is shown in red.
Is red an indication for a new measurement in general or is it a flag/is it counting as if I was cheating?
No worries! If it is new high in performance metrics it is shown in red. A new low in weight is also shown in red. Congratulations on your weight loss and Ride On!
Maybe your height is over 6’ and you are 50 years old? 
only kidding. It’s red probably because the height/weight/age difference is not inline with the statistical norm. Ignore it and have fun.