  Globular Clusters (GCs) are generally treated as natural validators of simple
stellar population (SSP) models. However, there are still some differences
between real GCs and SSPs. In this work we use a direct $N$-body simulation
code {\hf Nbody6} to study the influences of dynamical interactions,
metallicity and primordial binaries on Milky Way globular clusters' integrated
properties. Our models start with $N=100,000$ stars, covering a metallicity
range $Z=0.0001-0.02$, a subset of our models contain primordial binaries,
resulting in a binary fraction as currently observed at a model age of
GCs.Stellar evolution and external tidal field representative for an average
Milky Way GC are taken into consideration. The integrated colours and Lick
indices are calculated using BaSeL and Bluered stellar spectral libraries
separately.
  By including dynamical interactions, our model clusters show integrated
features (colours up to 0.01mag bluer, H$\beta$ up to 0.1\AA $ $ greater and
[MgFe]$'$ 0.05\AA $ $ smaller) making the clusters appear slightly younger than
the model clusters without dynamical interactions. This effect is caused mainly
by the preferential loss of low-mass stars which have a stronger contribution
to redder passbands as well as different spectral features compared to
higher-mass stars. In addition, this effect is larger at lower metallicities.
On the contrary, the incorporation of primordial binaries reduces this effect.
