It’s a good place – the discussions under sentences are to discuss those sentences. ;-)
In general tha falt liath agam would mean that you have (someone else’s?) gray hair in your possession, eg. kept somewhere in your drawer… while tha falt liath orm means that you have gray hair as a part of you, growing on your body.
See also the Aig, air agus ann an or The severed head article on the Akerbeltz wiki.