  Measurements of the QCD colour factors C_A and C_F and of the number of
active quark flavours n_f in the process e+e- -> hadrons at high energy are
presented. They are based on fits of O(alpha_S**2)+NLLA QCD calculations to
distributions of the event shape observables 1-T, C, B_T and B_W measured at
centre-of-mass energies from 14 GeV to 189 GeV. Hadronisation effects are
approximated with power correction calculations which also depend on the QCD
gauge structure. In this approach potential biases from hadronisation models
are reduced. Our results for individually measured quantities are n_f = 5.64 +-
1.35, C_A = 2.88 +- 0.27 and C_F = 1.45 +- 0.27 in good agreement with QCD
based on the SU(3) symmetry group where n_f=5 for the energies considered here,
C_A=3 and C_F=4/3. From simultaneous fits of C_A and C_F we find C_A = 2.84 +-
0.24 and C_F = 1.29 +- 0.18, which is also in good agreement with the QCD
expectation.
