2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/95890We show that color can leak from a QCD bag if we allow for pseudoscalar isoscalar singlet ($η'$) coupling at the surface. To enforce total confinement of color an additional boundary term is suggested. New relations between the $η'$ mass and decay constant and the QCD gluon condensates are derived and compared with the empirical parameters.7 pages, LaTeX, Nordita - 92/68 NHigh Energy Physics - PhenomenologyNuclear Theorytext