I read that hadrons are in colour singlet state and that gluons are not and that the colour singlet gluon is forbidden for the reason of making strong force a long range force otherwise (and that SU(3) has 8 generators and thus 8 gluons) but my question is: are mesons in a colour singlet state? If not they cant be allowed to be seen and if they are shouldn't they make the range of the force also long? (or not since they have a mass limiting their range through decaying?) Also the most used representation of the generators have 1/sqrt(2) (r anti r - b anti b) and also one like 1/sqrt(6) (r anti r + b anti b - 2 g anti g). but arent these also 'white' ? since if measured has colour - anti colour..